Short answers, pulled from the story.
Euhemerus was a Greek mythographer active in the late fourth century BC who served at the court of Cassander, the king of Macedon. He is best known for originating euhemerism, the theory that mythological gods were originally human kings and heroes.
Euhemerus's birthplace is disputed. Most modern scholars accept Messina in Sicily, though ancient sources also named Chios, Tegea, or Agrigentum.
In his Sacred History, or Hiera Anagraphe, Euhemerus described a voyage to an island called Panchaea, where a golden pillar in a temple of Zeus Triphylius recorded the births and deaths of the gods. The original text is lost and survives only through fragments quoted by later writers such as Diodorus Siculus, Eusebius, and Lactantius.
Euhemerism is the theory that myths are distorted accounts of real historical events, with mythological figures originally real people whose stories were altered through retelling. Bulfinch's Mythology calls this the historical interpretation of myth.
Euhemerus argued that the Greek gods, including Zeus, had originally been kings, heroes, conquerors, or benefactors who earned the veneration of their people. He pointed to a tomb of Zeus said to be shown to visitors near Knossos as proof that Zeus had once lived and died as a man.
Early Christian writers such as Lactantius used Euhemerus's belief that the gods were originally human to argue that the pagan gods were inferior to the Christian God. Lactantius also preserved substantial portions of Ennius's Latin translation of Euhemerus's work in his Divine Institutes.