Cyril Lucaris (1572-1638 AD) was the Ecumenical Patriarch of Constantinople at various points between 1612-1638 AD. His published letters, as well as a confession of faith published under his name, demonstrate that he was a Calvinist, who completely rejected the Orthodox faith as it is professed by the current Orthodox Church.
For example:
The Confession of Cyril Lucaris (1629 AD)
13 We believe that man is justified by faith and not by works. But when we say by faith, we understand the correlative or object of faith, which is the righteousness of Christ, which, as if by hand, faith apprehends and applies unto us for our salvation. This we say without any prejudice to good works, for truth itself teaches us that works must not be neglected, that they are necessary means to testify to our faith and confirm our calling. But that works are sufficient for our salvation, that they can enable one to appear before the tribunal of Christ and that of their own merit they can confer salvation, human frailty witnesses to be false; but the righteousness of Christ being applied to the penitent, alone justifies and saves the faithful.
This confession, and the controversy that it caused, was the impetus for the Synod of Jerusalem (1672 AD), which is universally binding on all Orthodox Christians, having been accepted by all Patriarchates.
The Synod attempted to address and refute the Confession of Cyril, point-by-point. However, it denied that Cyril himself authored the confession, which is historically untenable, as is documented at length in the video Cyril Lucaris: Calvinist Patriarch/Orthodox Saint, by AncientPathsTV. There is an extant signed copy of the confession by Cyril, and his letters likewise demonstrate that his beliefs aligned with those in the confession, and that he was active in disseminating those beliefs to those he ministered to.
However, despite denying that Cyril authored the confession, the Synod of Jerusalem declared that, regardless, Cyril was a "a wretch", "having no part with Christ":
The Acts and Decrees of the Synod of Jerusalem (1672 AD)
For neither let our adversaries boast with regard to Cyril, as though he were a Saint; for he was not killed unjustly, as they delight to say, or for the Name of Christ, that he should be so considered; but being possessed by the failing of an excessive ambition, which the great Basil recognised as the disease of Lucifer, having thrice unlawfully, in addition to the first time apparently lawfully, obtained possession of the Throne of Constantinople, with innumerable ejections and vexations of the Clergy (by his insatiate desire for external things, and availing himself of the help of the Dutch Ambassador, for which he became more liable to suspicion with the Church), he incurred that most disgraceful death. Whom, as having practised such things towards the Church of Christ, even though he had been Orthodox, we hold as a sinner, and such a sinner as should receive at the hands of God punishment for the evils which he had inflicted upon the Church of God without scruple; and now, since he is become an author of impiety, as our enemies affirm, we regard not as a Saint, but as a wretch, and as having no part with Christ.
Notice that the above states that "he was not killed unjustly, as they delight to say, or for the Name of Christ, that he should be so considered" - that is, he was not a martyr. Likewise, "we regard (him) not as a Saint, but as a wretch, and as having no part with Christ".
Yet, in spite of the above, on October 6, 2009, Patriarch Theodore II of Alexandria (1954 AD) canonized Cyril as a Saint and martyr:
Canonization of Saint Cyril Lucaris (2009 AD)
Therefore, we unanimously decide, we decree and appoint, and we pass on in the Holy Spirit, that from now on and for all time to come, the pre-eminent and eternal Patriarch Cyril, called Lucaris, is numbered among the choir of the Holy Hierarchs and Martyrs of the Church, being honored with annual rites and sanctifications by the pious multitude of the faithful, and being celebrated with hymns, songs, and praises on the 27th of June, on the day his martyrdom was completed, in honor of him, and the glory of the one who is in To the saints of our wondrous God, who glorifies the Saints and is glorified in their holy monuments and shrines, a feast day. And in evidence and confirmation of this, our present Patriarchal and Synodal Act was made, established and signed in the holy Code of our Most Holy Church of Alexandria.
In the year of salvation two thousand and nine, in the month of October, on the sixth.
Theodore II of Alexandria (source)
Additionally, on January 11, 2022, the Ecumenical Patriarch of Constantinople Bartholomew (1940 AD) canonized Cyril, adding his name to the Orthodox Church's hagiography:
Orthodoxia - April-June 2023, pg. 132
55 It should be noted that Patriarchs Jeremiah I, Cyril Lucaris and Cyril VI were canonized in the Hagiography of the Orthodox Church under the Patriarchate of Bartholomew, the decisions to this effect having been taken at the sessions of January 10, 2023, and January 11, 2022, respectively, on the recommendation of the Canonical Commission through its reports of January 6, 2023 and January 10, 2022. The Patriarchal and Synodal Acts to this effect were recorded in the Code of the Great Church: AB΄12, pp. 48-51, 52-55 and 80-81. (source)
Therefore, according to at least two modern Patriarchs of the Eastern Orthodox Church, Cyril Lucaris was a Saint, even though the Synod of Jerusalem explicitly regarded him as a non-Saint, who "we hold as a sinner, and such a sinner as should receive at the hands of God punishment for the evils which he had inflicted upon the Church of God without scruple", and one "having no part with Christ".
The Eastern Orthodox Church attempted to rewrite history at the Synod of Jerusalem, claiming that Cyril was not a Calvinist. The aforementioned documentary, which inspired this article, demonstrates that this is a plain attempt at historical revisionism by the Synod - a Synod which is held by Orthodox Christians to have been guided by the Holy Spirit, and infallible.
Additionally, the modern Eastern Orthodox Church contradicts itself, by canonizing a person who was explicitly declared to be an impious, unsaintly individual by the Synod of Jerusalem.