Rhadamanthus, also known as Rhadamanthys, is a son of Zeus and Europa and a major figure in Greek mythology. He was considered a demigod due to his father being Zeus and his name means showing stern and inflexible judgement. He was a wise king of Crete who, after death, became one of the judges of the dead in the Greek underworld, Hades. He was to be the judge of souls from eastern regions and, along with Aeacus and Minos, would judge damned souls and determine their punishment in the afterlife.
Rhadamanthus is Eikichi Mishina's initial Persona. His first appearance in the game occurs when Eikichi uses him to attack Tatsuya Suou and Lisa Silverman in Sumaru Prison, indicating that he was already aware of the existence of his Persona beforehand - however, Eikichi mistakenly referred to his Persona as a shinigami ("Grim Reaper"/"Death God"/"Deathbringer" in the official release), and is shocked when Tatsuya and Lisa summon their "shinigami" in response. It was not until he, Tatsuya and Lisa met Philemon that he learned more about the true nature of what his Persona really was.