He is the co-creator of the Adult Swim animated series Aqua Teen Hunger Force, Squidbillies, and Your Pretty Face Is Going to Hell.

Willis has worked on various Adult Swim shows that are created primarily by Williams Street, an animation-centered, Atlanta-based production division of Cartoon Network.

Willis got hired at Ghost Planet Industries after giving the producers a very formal letter of recommendation written in crayon, seemingly by a young child.

Aqua Teen Hunger Force first premiered unannounced in the early hours of December 30, 2000 and later officially debuted on Adult Swim in the Fall of 2001.

In 2010, Willis created Cheyenne Cinnamon and the Fantabulous Unicorn of Sugar Town Candy Fudge, a new television pilot for Adult Swim.