Aristides Demetrios was a famed archaeologist in Greece who discovered an ancient artifact known as the golden fleece. This fabric had absorbed the superhuman abilities of fifty of history's heroes, which Aristides used in his alter ego as the Olympian, protector of Greece.
Marcus was a champion of people who in ancient history opposed to the Greek armies of legend. He was tied to an even older heritage as the latest in the long line of heroes known as Immortal Man, that would possess superhuman powers and the minds of historical champions.
While Aristides only appeared beside Wonder Woman and later with his fellow Global Guardians aided by Superman and his Super Friends on two cases, Marcus would have a more profound history as Immortal Man, albeit with only a few of his tales told.