The prize is the third-largest ever in U.S. history.
Officials say there have been 11 winning jackpots of $500 million or more since Mega Millions began in 2002.
"I know I want to own a bus," said the winner in the Sith Lord getup.
"I'm pretty laid back and don't spend money on expensive things," the Delaware "Lucky for Life" winner told a newspaper.
The winning numbers were 8, 12, 13, 19 and 27. The Powerball is 4.