Justin Martyr was a Christian apologist and a martyr. He was beheaded for his faith around 165 AD at the behest of emperor Marcus Aurelius. He is mentioned in multiple sources of antiquity and a large body of his work survives to this day.
He was a philosopher who had experimented with Stoicism, Pythagoreanism and Platonism. Justin was converted to Christ around 132 AD after being urged to turn to the Jewish scriptures. In his "apologies" (from the Greek plural apologia, singular apologion, "explanations") to the emperor Antoninus Pius and the Roman Senate, he argued that the truth found in Greek philosophy prefigured some of the teachings of Christ. He also wrote Dialogue with Trypho, a debate between Justin and a Jew arguing that Christianity was the fulfillment of Judaism. Justin traveled extensively throughout the Roman Empire in evangelistic efforts.
McDowell, Josh. Evidence for Christianity. Thomas Nelson, Inc. 2006.