Umar ibn al-Khattab joined Muhammad in the early days of his preaching, before the Hijra to Medina. He would become instrumental in the early spread of Islam (Sahih al-Bukhari 3863), and became the second Caliph after Abu Bakr died. Muhammad said that if there had been a prophet after him, it would have been Umar (Jami at-Tirmidhi 3686).
He was known as somewhat of a harsh, aggressive thug, even amongst Muhammad's band of merry men, and there are multiple narrations that show his aggressive behavior, and the fact that others feared him:
Sahih al-Bukhari 4992
Narrated `Umar bin Al-Khattab:
I heard Hisham bin Hakim reciting Surat Al-Furqan during the lifetime of Allah's Messenger (ﷺ) and I listened to his recitation and noticed that he recited in several different ways which Allah's Messenger (ﷺ) had not taught me. I was about to jump over him during his prayer, but I controlled my temper, and when he had completed his prayer, I put his upper garment around his neck and seized him by it and said, "Who taught you this Sura which I heard you reciting?" He replied, "Allah's Messenger (ﷺ) taught it to me." I said, "You have told a lie, for Allah's Messenger (ﷺ) has taught it to me in a different way from yours."
So I dragged him to Allah's Messenger (ﷺ) and said (to Allah's Messenger (ﷺ)), "I heard this person reciting Surat Al-Furqan in a way which you haven't taught me!" On that Allah's Apostle said, "Release him, (O `Umar!) Recite, O Hisham!" Then he recited in the same way as I heard him reciting. Then Allah's Messenger (ﷺ) said, "It was revealed in this way," and added, "Recite, O `Umar!" I recited it as he had taught me. Allah's Messenger (ﷺ) then said, "It was revealed in this way. This Qur'an has been revealed to be recited in seven different ways, so recite of it whichever (way) is easier for you (or read as much of it as may be easy for you).
Sahih Muslim 1478
He (Hadrat 'Umar) said: I would say something which would make the Prophet (ﷺ) laugh, so he said: Messenger of Allah, I wish you had seen (the treatment meted out to) the daughter of Khadija when she asked me some money, and I got up and slapped her on her neck. Allah's Messenger (may peace be upon him) laughed and said: They are around me as you see, asking for extra money.
Abu Bakr (Allah be pleased with him) then got up went to 'A'isha (Allah be pleased with her) and slapped her on the neck, and Umar stood up before Hafsa and slapped her saying: You ask Allah's Messenger (ﷺ) which he does not possess. They said: By Allah, we do not ask Allah's Messenger (ﷺ) for anything he does not possess. Then he withdrew from them for a month or for twenty-nine days. Then this verse was revealed to him:" Prophet: Say to thy wives... for a mighty reward" (Surah 33:28-29).
Sunan ibn-Majah 1985
It was narrated that Iyas bin 'Abdullah bin Abu Dhubab said:
"The Prophet said: 'Do not beat the female slaves of Allah.' Then 'Umar came to the Prophet and said: 'O Messenger of Allah, the woman have become bold towards their husbands? So order the beating of them,' and they were beaten. Then many women went around to the family of Muhammad. The next day he said: 'Last night seventy women came to the family of Muhammad, each woman complaining about her husband. You will not find that those are the best of you.'"
Sunan ibn-Majah 1986
It was narrated that Ash'ath bin Qais said:
"I was a guest (at the home) of 'Umar one night, and in the middle of the night he went and hit his wife, and I separated them. When he went to bed he said to me: 'O Ash'ath, learn from me something that I heard from the Messenger of Allah" A man should not be asked why he beats his wife, and do not go to sleep until you have prayed the Witr."' And I forgot the third thing."
Sahih al-Bukhari 1304
Narrated `Abdullah bin Umar:
Sa`d bin 'Ubada became sick and the Prophet (ﷺ) along with `Abdur Rahman bin `Auf, Sa`d bin Abi Waqqas and `Abdullah bin Mas`ud visited him to inquire about his health. When he came to him, he found him surrounded by his household and he asked, "Has he died?" They said, "No, O Allah's Apostle." The Prophet (ﷺ) wept and when the people saw the weeping of Allah's Messenger (ﷺ) (p.b.u.h) they all wept. He said, "Will you listen? Allah does not punish for shedding tears, nor for the grief of the heart but he punishes or bestows His Mercy because of this." He pointed to his tongue and added, "The deceased is punished for the wailing of his relatives over him." Umar used to beat with a stick and throw stones and put dust over the faces (of those who used to wail over the dead).
Sahih Muslim 31
So when I came to this garden, I drew myself together as a fox does, and these people are following me. He addressed me as Abu Huraira and gave me his sandals and said: Take away these sandals of mine, and when you meet anyone outside this garden who testifies that there is no god but Allah, being assured of it in his heart, gladden him by announcing that he shall go to Paradise. Now the first one I met was Umar. He asked: What are these sandals, Abu Huraira? I replied: These are the sandals of the Messenger of Allah with which he has sent me to gladden anyone I meet who testifies that there is no god but Allah, being assured of it in his heart, with the announcement that he would go to Paradise. Thereupon Umar struck me on the breast and I fell on my back.
He then said: Go back, Abu Huraira, So I returned to the Messenger of Allah (ﷺ), and was about to break into tears. 'Umar followed me closely and there he was behind me. The Messenger of Allah (may peace and blessings be on him) said: What is the matter with you, Abu Huraira? I said: I happened to meet 'Umar and conveyed to him the message with which you sent me. He struck me on my breast which made me fall down upon my back and ordered me to go back. Upon this the Messenger of Allah (ﷺ) said: What prompted you to do this, 'Umar? He said: Messenger of Allah, my mother and father be sacrificed to thee, did you send Abu Huraira with your sandals to gladden anyone he met and who testified that there is no god but Allah, and being assured of it in his heart, with the tidings that he would go to Paradise? He said: Yes. Umar said: Please do it not, for I am afraid that people will trust in it alone; let them go on doing (good) deeds. The Messenger of Allah (ﷺ) said: Well, let them.
Notice above that he knocks someone to the ground for relaying a revelation from Muhammad. He then tells Muhammad not to relay that revelation, because of its practical implications. Later, we see Muhammad adopting this view, and telling people not to relay the message (Sahih Muslim 30b, 32).
Continuing the narrations evidencing Umar's thuggish behavior and reputation:
Sahih al-Bukhari 5843
Narrated Ibn `Abbas:
For one year I wanted to ask Umar about the two women who helped each other against the Prophet (ﷺ) but I was afraid of him.
...
Sahih al-Bukhari 6085
Narrated Sa`d:
Umar bin Al-Khattab asked permission of Allah's Messenger (ﷺ) to see him while some Quraishi women were sitting with him and they were asking him to give them more financial support while raising their voices over the voice of the Prophet. When `Umar asked permission to enter, all of them hurried to screen themselves. The Prophet (ﷺ) admitted `Umar and he entered, while the Prophet (ﷺ) was smiling. `Umar said, "May Allah always keep you smiling, O Allah's Messenger (ﷺ)! Let my father and mother be sacrificed for you !"
The Prophet (ﷺ) said, "I am astonished at these women who were with me. As soon as they heard your voice, they hastened to screen themselves." `Umar said, "You have more right, that they should be afraid of you, O Allah's Messenger (ﷺ)!" And then he (`Umar) turned towards them and said, "O enemies of your souls! You are afraid of me and not of Allah's Messenger (ﷺ)?" The women replied, "Yes, for you are sterner and harsher than Allah's Messenger (ﷺ)." Allah's Messenger (ﷺ) said, "O Ibn Al-Khattab! By Him in Whose Hands my life is, whenever Satan sees you taking a way, he follows a way other than yours!"
In the above, Muhammad says that even Satan himself was afraid of Umar, and found it amusing that the women he was with were terrified of him. What kind of behavior would someone have to engage in so that Ibn Abbas put off asking him a question for a year, and women hurriedly went to comply with his preferences when they knew he was coming? Allow me to ask you - what would someone have to do to you, or what would you have to hear of them, to make you behave that way?
There are also ample narrations in which he stated his willingness to chop someone's head off:
Sahih al-Bukhari 3610
Narrated Abu Sa`id Al-Khudri:
While we were with Allah's Messenger (ﷺ) who was distributing (i.e. some property), there came Dhu-l- Khuwaisira, a man from the tribe of Bani Tamim and said, "O Allah's Messenger (ﷺ)! Do Justice." The Prophet said, "Woe to you! Who could do justice if I did not? I would be a desperate loser if I did not do justice." Umar said, "O Allah's Messenger (ﷺ)! Allow me to chop his head off." The Prophet (ﷺ) said, "Leave him, for he has companions who pray and fast in such a way that you will consider your fasting negligible in comparison to theirs.
Sahih al-Bukhari 4095
Narrated Jabir bin `Abdullah:
We were in a Ghazwa (Sufyan once said, in an army) and a man from the emigrants kicked an Ansari man (on the buttocks with his foot). The Ansari man said, "O the Ansar! (Help!)" and the emigrant said. "O the emigrants! (Help!) Allah's Messenger (ﷺ) heard that and said, "What is this call for, which is characteristic of the period of ignorance?" They said, "O Allah's Messenger (ﷺ)! A man from the emigrants kicked one of the Ansar (on the buttocks with his foot)." Allah's Messenger (ﷺ) said, "Leave it (that call) as is a detestable thing." `Abdullah bin Ubai heard that and said, 'Have the (the emigrants) done so? By Allah, if we return Medina, surely, the more honorable will expel therefrom the meaner." When this statement reached the Prophet. Umar got up an, said, "O Allah's Messenger (ﷺ)! Let me chop off the head of this hypocrite (`Abdullah bin Ubai)!" The Prophet (ﷺ) said "Leave him, lest the people say that Muhammad kills his companions." The Ansar were then more in number than the emigrants when the latter came to Medina, but later on the emigrant increased.
Sahih al-Bukhari 1354-55
Narrated Ibn `Umar:
`Umar set out along with the Prophet with a group of people to Ibn Saiyad till they saw him playing with the boys near the hillocks of Bani Mughala. Ibn Saiyad at that time was nearing his puberty and did not notice (us) until the Prophet (ﷺ) stroked him with his hand and said to him, "Do you testify that I am Allah's Messenger (ﷺ)?" Ibn Saiyad looked at him and said, "I testify that you are the Messenger of illiterates."
Then Ibn Saiyad asked the Prophet, "Do you testify that I am Allah's Messenger (ﷺ)?" The Prophet refuted it and said, "I believe in Allah and His Apostles." Then he said (to Ibn Saiyad), "What do you think?" Ibn Saiyad answered, "True people and liars visit me." The Prophet (ﷺ) said, "You have been confused as to this matter." Then the Prophet (ﷺ) said to him, "I have kept something (in my mind) for you, (can you tell me that?)" Ibn Saiyad said, "It is Al-Dukh (the smoke)." The Prophet (ﷺ) said, "Let you be in ignominy. You cannot cross your limits." On that Umar, said, "O Allah's Messenger (ﷺ)! Allow me to chop his head off." The Prophet said, "If he is he (i.e. Dajjal), then you cannot overpower him, and if he is not, then there is no use of murdering him."
(Ibn `Umar added): Later on Allah's Messenger (ﷺ) once again went along with Ubai bin Ka`b to the date-palm trees (garden) where Ibn Saiyad was staying. The Prophet wanted to hear something from Ibn Saiyad before Ibn Saiyad could see him, and the Prophet saw him lying covered with a sheet and from where his murmurs were heard. Ibn Saiyad's mother saw Allah's Apostle while he was hiding himself behind the trunks of the date-palm trees. She addressed Ibn Saiyad, "O Saf! (and this was the name of Ibn Saiyad) Here is Muhammad." And with that Ibn Saiyad got up. The Prophet (ﷺ) said, "Had this woman left him (Had she not disturbed him), then Ibn Saiyad would have revealed the reality of his case.
Notice the overall strangeness of the last passage above, in particular. Muhammad thinks that an adolescent boy named Ibn Saiyad could be the Dajjal - once again proving that he taught the end was imminently near. Yet, how does he ascertain whether the boy is the Dajjal? Does he pray to Allah for answers? No, rather he asks the boy if he can read his mind, and later on, he is caught spying on the boy by his mother. And, of course, because the boy - who is mentioned in very many Hadiths (Sahih al-Bukhari 2638, 3055-57, 6172-75, 6618) - did not show sufficient respect to Muhammad, Umar wanted to cut his head off.
After examining the above, we have a good idea of Umar's character. He was a murderous, violent, thug.
The first narration that demonstrates Umar's influence on Muhammad is one in which he corrects Muhammad's error, which leads directly to Surah 9:84 being revealed:
Sahih al-Bukhari 5796
Narrated `Abdullah bin `Umar:
When `Abdullah bin Ubdi (bin Salul) died, his son came to Allah's Messenger (ﷺ) and said ' O Allah's Apostle, give me your shirt so that I may shroud my fathers body in it. And please offer a funeral prayer for him and invoke Allah for his forgiveness." The Prophet (ﷺ) gave him his shirt and said to him 'Inform us when you finish (and the funeral procession is ready) call us. When he had finished he told the Prophet (ﷺ) and the Prophet (ﷺ) proceeded to order his funeral prayers but `Umar stopped him and said, "Didn't Allah forbid you to offer the funeral prayer for the hypocrites when He said: "Whether you (O Muhammad) ask forgiveness for them or ask not forgiveness for them: (and even) if you ask forgiveness for them seventy times. Allah will not forgive them." (9.80) Then there was revealed: "And never (O Muhammad) pray for any of them that dies, nor stand at his grave." (9.84) Thenceforth the Prophet (ﷺ) did not offer funeral prayers for the hypocrites.
This is also narrated in Sahih al-Bukhari 1366. Muhammad was going to offer the funeral prayer, but Umar stopped him, citing a verse in the Quran. Then, "Allah" revealed essentially Umar's words to Muhammad, as a new verse in the Quran.
Next, we can see that Umar wanted women to be veiled, yet Muhammad didn't see the need to "reveal" that rule. Umar then harasses one of Muhammad's wives, and lo, a new verse of the Quran is revealed to implement what he wanted:
Sahih Muslim 2170d
'A'isha reported that the wives of Allah's Messenger (ﷺ) used to go out in the cover of night when they went to open fields (in the outskirts of Medina) for easing themselves. 'Umar b Khattab used to say:
Allah's Messenger, ask your ladies to observe veil, but Allah's Messenger (ﷺ) did not do that. So there went out Sauda, daughter of Zarn'a, the wife of Allah's Messenger (ﷺ), during one of the nights when it was dark. She was a tall statured lady. 'Umar called her saying: Sauda, we recognise you. (He did this with the hope that the verses pertaining to veil would be revealed.) 'A'isha said: Allah, the Exalted and Glorious, then revealed the verses pertaining to veil.
This is also narrated in Sahih al-Bukhari 146.
Umar later reflected on the fact that not only was veiling "revealed" in accordance with his will, but also two other verses, one of which (Surah 66:5) is his own words:
Sahih al-Bukhari 402
Narrated `Umar (bin Al-Khattab):
My Lord agreed with me in three things:
1. I said, "O Allah's Messenger (ﷺ), I wish we took the station of Abraham as our praying place (for some of our prayers). So came the Divine Inspiration: And take you (people) the station of Abraham as a place of prayer (for some of your prayers e.g. two rak`at of Tawaf of Ka`ba)". (Surah 2:125)
2. And as regards the (verse of) the veiling of the women, I said, 'O Allah's Messenger (ﷺ)! I wish you ordered your wives to cover themselves from the men because good and bad ones talk to them.' So the verse of the veiling of the women was revealed. (Surah 33:59)
3. Once the wives of the Prophet (ﷺ) made a united front against the Prophet (ﷺ) and I said to them, 'It may be if he (the Prophet) divorced you, (all) that his Lord (Allah) will give him instead of you wives better than you.' So this verse (the same as I had said) was revealed." (Surah 66:5).
The above is also narrated in Sahih al-Bukhari 4483, 4916.
Isn't it incredible how Umar was able to bend Allah to reveal the stuff that he wanted to be implemented? It's evident from narrations like this that Muhammad is Allah, and Umar is influencing Muhammad with his behavior.
Another narration which exemplifies this pertains to Umar wanting to get alcohol banned, and pestering Muhammad as he "reveals" progressively stricter rules regarding alcohol until there is total prohibition:
Sunan abu-Dawud 3670
Narrated Umar ibn al-Khattab:
When the prohibition of wine (was yet to be) declared, Umar said: O Allah, give us a satisfactory explanation about wine. So the following verse of Surat al-Baqarah revealed; "They ask thee concerning wine and gambling. Say: In them is great sin...." Umar was then called and it was recited to him.
He said: O Allah, give us a satisfactory explanation about wine. Then the following verse of Surat an-Nisa' was revealed: "O ye who believe! approach not prayers with a mind befogged...." Thereafter the herald of the Messenger of Allah (ﷺ) would call when the (congregational) prayer was performed: Beware, one who is drunk should not come to prayer. Umar was again called and it was recited to him).
He said: O Allah, give us a satisfactory explanation about wine. This verse was revealed: "Will ye not then abstain?" Umar said: We abstained.
Above, we see plainly that Umar is writing the Quran. Each time he doesn't like what's "revealed", Muhammad gets a new "revelation" until Umar is satisfied.
The development of the verses above on alcohol are as follows:
Surah 2:219
219 They ask you ˹O Prophet˺ about intoxicants and gambling. Say, “There is great evil in both, as well as some benefit for people—but the evil outweighs the benefit.”
Surah 4:43
43 O believers! Do not approach prayer while intoxicated until you are aware of what you say, nor in a state of ˹full˺ impurity—unless you merely pass through ˹the mosque˺—until you have bathed.
Surah 5:90-91
90 O believers! Intoxicants, gambling, idols, and drawing lots for decisions are all evil of Satan’s handiwork. So shun them so you may be successful.
91 Satan’s plan is to stir up hostility and hatred between you with intoxicants and gambling and to prevent you from remembering Allah and praying. Will you not then abstain?
First, it's potentially bad, but could be good, yet should be avoided. Then, just make sure you aren't showing up to prayer drunk. Finally, don't take any intoxicants - they are all evil and Satan's handiwork - abstain.
Clearly, there is a gradient of less strict, to more strict, to banned altogether. It's amazing that "Allah" couldn't have started with the last verse in his "eternal word", but instead had to abrogate two other verses before "he" (Umar, Muhammad, whatever) got it right.
Allah seemed to be reacting in real-time to the whims of one of Muhammad's most disagreeable, vile companions. Umar's desires have been immortalized in the Quran, which is an all-too-human revelation from the mind of a 7th century man named Muhammad.