Voltaire and Diderot, Enlightenment figures sure enough, venerated Socrates. What did they find in or get from him ? Crucially the Enlightenment celebrated reason and virtue; and Socrates was seen to embody both to the highest degree.
There is a useful passage in Miriam Leonard, 'Greeks, Jews, and the Enlightenment : Moses Mendelssohn's Socrates', Cultural Critique, No. 74, CLASSICAL RECEPTION AND THE POLITICAL (Winter 2010), p.185 :
If the twentieth century, in the wake of Freud's compelling reading of Sophocles, has been known as the "age of Oedipus," the eighteenth century could be called the age of Socrates (see Böhm; Trapp 2007b; Trousson; Viellard-Baron). The Enlightenment witnesses what Raymond Trousson has called a "prise de conscience 'socratique'". As intellectuals across Europe sought to associate their endeavors with the Athenian sage, Socrates was transformed into a figure of modernity. But those, like Voltaire, Rousseau, and Diderot, who wanted to make of Socrates a paradigm of reason had to contend with a tenacious tradition that linked Socrates to the figure of Christ. Long before Percy Bysshe Shelley proclaimed Socrates "the Jesus Christ of Greece," Christian writers had been drawn to accounts of Socrates' death as a precursor to Christ's own agony. The specter of a thousand dying Christs looms behind even Jacques-Louis David's aggressively secular Death of Socrates. The age of reason may have worked hard to topple Jesus Christ from his position of authority and replace him with the pagan Socrates, but this effort more often than not resulted in an insidious juxtaposition rather than a straightforward substitution. It was Voltaire, after all, who named Christ the "Socrates of Palestine" (see Goulbourne; Wilson).
In the Jewish Enlightenment - the Jewish contribution to the Enlightenment - Moses Mendelssohn (1729-86) was widely referred to as 'the German Socrates'. We might note that Mendelssohn found enough interest and illumination in Homer and Aesop to write essays on them.
▻ PLATO AND ARISTOTLE
Plato seems not to have been a central influence except as a conduit through his dialogues of (what were taken to be) Socrates' ideas. Aristotle's reputation was under a cloud because of the rejection of Aristotelianism in the Scientific Revolution of the 16th and 17th centuries, a revolution which the Enlightenment celebrated.
A Roman, of course, but the Latin voice of the Greek philosopher, Epicurus. Lucretius's 'De Rerum Natura' [On the Nature of Things] was an Enlightenment favourite because, in place of Christian assurances about a problematic life after death, and the grip of age-old fear of death, it denied that death was an evil. Everything should be focused on 'this' life : our pre-natal non-existence was nothing to us before we were born and equally our post mortem non-existence will be nothing to us after our death. When we are alive, we have the experience of being alive; when we are dead we will have no experience of being dead. (I think the argument is flawed but that doesn't matter here.)
Another Roman but also an exponent of Greek Stoicism and hence a conduit through which Greek philosophy penetrated the Enlightenment. Let D'Alembert, as important an Enlightenment figure as Voltaire and Diderot, speak for himself : 'In philosophy logic should be limited to a few lines; metaphysics to an abridgement of Locke, purely philosophical ethics to the work of Seneca' (Peter Gay, 'The Enlightenment : An Interpretation', NY : W.W. Norton, 1977, p.510.)
Goulbourne, Russell. 2007. 'Voltaire's Socrates'. In Trapp, 'Socrates from Antiquity to the Enlightenment', 229-47.
Trapp, Michael. 2007. 'Socrates from Antiquity to the Enlightenment'. Aldershot:
Wilson, Emily. 2007. 'The Death of Socrates'. Cambridge, Mass.: Harvard University
Peter Gay, 'The Enlightenment : An Interpretation', NY : W.W. Norton, 1977.