Top Hat is the founder of the entire Evil Corporation and Beret's brother. In the last department of the game, the 'Department of Evil', Top Hat causes mischief and mayhem for Beret. He is the final boss of the game. Once Top Hat is defeated, you will be able to press 't' while playing any level to play as Top Hat.
"He's a jerk, but so am I. As the creator of the Evil Corporation, you could view him as the in-game version of me if you want." - KiwisauceY