Not much is known of Aristides, a second century Apologist. All we know of this early saint comes to us from some fragments in Eusebius and Jerome, who tell us that Aristides was a pagan philosopher of Athens until his conversion to Christianity. Eusebius and Jerome tell us that Aristides composed a lengthy apologia in defense of the Christian Faith which he delivered to the Emperor Hadrian sometime prior to 134, when it is believed Aristides died. Some have suggested his apology dates from the time of Antoninus Pius, but most scholars prefer the era of Hadrian. If so, this would make Aristides' work the oldest Christian apologetic work, predating that of Quadratus by several years.
Only fragments of Aristides' work survived until a complete Syriac translation was discovered in 1899. Aristides divides the world into four races (a) barbarians (b) Greeks (including Egyptians and Chaldeans) (c) Jews (d) Christians. He then proceeds to examine the religions and beliefs of each group, starting with the barbarians who are furthest from the truth and then proceeding up to the Christians, who possess the fullness of truth.
The place and manner of his death are uncertain, but his Feast Day is celebrated on August 31st.
Apology of Aristides the Philosopher is available online here.