St. Justin Martyr says that those before Christ who followed reason (the Logos) were Christians (Christ is the divine Logos)–he even gives Socrates as an example!
Chapter 46. The Word in the world before Christ
But lest some should, without reason, and for the perversion of what we teach, maintain that we say that Christ was born one hundred and fifty years ago under Cyrenius, and subsequently, in the time of Pontius Pilate, taught what we say He taught; and should cry out against us as though all men who were born before Him were irresponsible — let us anticipate and solve the difficulty. We have been taught that Christ is the first-born of God, and we have declared above that He is the Word of whom every race of men were partakers; and those who lived reasonably are Christians, even though they have been thought atheists; as, among the Greeks, Socrates and Heraclitus, and men like them; and among the barbarians, Abraham, and Ananias, and Azarias, and Misael, and Elias, and many others whose actions and names we now decline to recount, because we know it would be tedious. So that even they who lived before Christ, and lived without reason, were wicked and hostile to Christ, and slew those who lived reasonably. But who, through the power of the Word, according to the will of God the Father and Lord of all, He was born of a virgin as a man, and was named Jesus, and was crucified, and died, and rose again, and ascended into heaven, an intelligent man will be able to comprehend from what has been already so largely said. And we, since the proof of this subject is less needful now, will pass for the present to the proof of those things which are urgent.