As outlined by numerous Fathers of the Church, Christ was the expectation of all the nations, and as such, many of the writings from disperate cultures throughout the world tell of and indicate the great Redeemer of the whole world Who was to come: Jesus Christ.
Many of the philosophers of ancient Greece seem to point towards Christ in their writings, and thus many Greeks were primed, in a certain sense, to accept the teachings of Christ's apostles. The picture above is part of a series of icons from the Great Meteora Monastery that depict St. Paul and St. Justin the Philosopher leading Greeks to Christ while citing Greek Philosophy. On either side are depicted many ancient Greek philosophers, and quotes from their writings that seem to point to Christ. (It is worth noting that they put a small fence around these icons, most likely that they might not be venerated like icons of the Saints.)
These are newly-painted icons, but they are by no means out of tradition. The "Hermenia" or Painter's Manual by Monk Dionysios of Fourna mentions the names, descriptions and quotes of such philosophers. The Monasteries of Megiste Lavra and Vatopedi on Mount Athos (as examples) also have depictions of such philosophers.
We can see vividly how God works to lead all nations to the Truth. Though their examples pale in comparison to the love, grace and sacrifice of Christ and His Saints, these philosophers help us understand the human condition, and how our longing can only be satiated by Christ.
The following Greek quotes from the depicted philosophers are from http://enaskitis.blogspot.com/2011/09/blog-post.html, along with my own amateur translations. If you have any suggestions for better translations, or can provide a documented translation or a citation from the philosophers' original writings, please share.
“Η Έλληνίς Σίβυλλα η φιλόσοφος” : “Ήξει ουρανόθεν βασιλεύς αιώνων ο μέλλων κρίναι πάσαν σάρκα και κόσμον άπαντα”.
The Greek Sybil, the Philosopher: "The eternal king has come from heaven, who will judge all flesh and the whole world."
For more on the Sybil of Erythrae foreshadowing Christ, see: http://full-of-grace-and-truth.blogspot.com/2010/01/sibyl-of-erythrae-and-prophetic.html.
“Ο Έλλην Σόλων ο σοφός και νομοθέτης” : “Ήν δ’ αυτός τώι αυτοπάτορι απάτωρ τρισόλβιος ός [sic: ως] τι φως τριλαμπές ο δε παθών Θεός εστι και ου θεότης πάθεν όστις φως γαρ, βροτόσωμος αυτός Θεός ήδη και ανήρ πάντως φέρων εν θνητοίς”.
The Greek Solon, the Wise and Law-giver: "Being himself the fatherless father, thrice-praised and thrice-radiant as the light, it is God who suffers and not godhead which suffers, who therefore is light, this mortal-body is God, and man always bringing among mortals.
“Ο Έλλην Πυθαγόρας ο φιλόσοφος και μαθηματικός” : “Ο Θεός εστιν νους και λόγος και πνεύμα και λόγος [bis] σαρκωθείς εκ Πατρός”.
The Greek Pythagoras, the Philosopher and Mathematician: "God is nous and word and spirit and word incarnate from the Father."
“O Έλλην Σωκράτης ο φιλόσοφος” : “Και το όνομα αυτού αυξηθήσεται και τιμηθήσεται υπό πάντων εφ’ όλην την οικουμένην”.
The Greek Socrates the Philosopher: "And his name will be increased and honored by all throughout the world."
“Ο Έλλην Απολλώνιος ο φιλόσοφος” : “Ένα Θεόν ύψιστον εν τρισίν λέγω, ός ουρανόν έρξεν άμα και χθόνα, Θεός ήν μεν αεί και εστίν και έσται ούτε αρξάμενος, ούτε παυσόμενος”.
The Greek Apollon, the Philosopher: "I speak of one God exalted in three, who created heaven and earth, God ever was and is and will be, neither changed, nor ceasing."