After Fox approved the project, James L. Brooks and Matt Groening began choosing voice actors for the major characters. They didn’t have to look far; Tracey Ullman castmembers Dan Castellaneta and Julie Kavner were chosen to voice Homer and Marge Simpson. While Dan Castellaneta had previous voice over experience, Julie Kavner did not. Most importantly, however, both of them were already under contract to Fox.
Nancy Cartwright had been a veteran voice actor and was brought in to test for Lisa Simpson. After reading the script, Nancy decided that she wanted to be Bart- not Lisa. Despite their original doubts, Matt and Albert knew she was the right voice for Bart Simpson.
With most of the family cast, that just left Lisa Simpson. Yeardley Smith, who had not done much work up until then, was called in to read for Lisa. She had originally thought the role would be a one off, but she quickly realized it would be a much bigger project.
With the main characters now properly voiced, production started on what would become 48 one minute shorts. Crudely drawn and produced, the shorts quickly gained a cult following. As Matt Groening’s Life in Hell fans discovered the shorts, they quickly outshone The Tracey Ullman Show itself. Could Fox turn this crudely drawn filler material into something bigger? They thought they could.