Lycaon
Λυκάων
The Arcadian king turned into a wolf for testing a god.
To test whether the stranger at his door was really Zeus, he cooked human flesh and served it.
When Zeus brought the house down, he fled into the fields — and as he tried to howl, found he had become a wolf.
Enraged by this, Zeus decided to drown humanity in a flood — the story of Deucalion follows from here.
SourcesOvid, Metamorphoses