In this comeback year for investors, David Tepper may have scored one of the biggest paydays of all.Mr. Tepper's hedge-fund firm has racked up about $7 billion of profit so far this year—with Mr. Tepper on track to earn more than $2.5 billion for himself, according to people familiar with the matter. That is among the largest one-year takes in recent years. Behind the wins: a bet worth billions of dollars that America would avoid a repeat of the Great Depression.Through February and March, Mr. Tepper scooped up beaten-down bank shares as many investors were running for the exits. Day...