The name 'Bugs Bunny' originated from animator Charles Thorson writing 'Bugs's Bunny' on a character model sheet in 1939.

According to Wikipedia's account of Bugs Bunny's history, the rabbit's third appearance in Hare-um Scare-um (1939) was the first to depict him as a gray bunny. Charles Thorson, the lead animator on that film, had written 'Bugs's Bunny' on the model sheet he drew for director Ben Hardaway. The name stuck, and promotional material later dropped the apostrophe and possessive form, letting 'Bugs Bunny' become the character's official name. It is a small detail that reveals how much of animation history depends on informal, human moments — a pencil scribble on a drawing sheet.