As we mourn the loss of The Simpsons' co-creator Sam Simon, who died Sunday (March 8) at the age of 59, we're paying tribute to him and the beloved show by looking back at our favorite pop star cameos from the series.

Simon, who passed away after a battle with colon cancer, gave away the majority of his $100 million fortune, mostly to animal-friendly charities that he supported. In addition to his incredible generosity, Simon — who left The Simpsons after Season 4 — is credited with helping to shape the show and turn it into the classic that it is today.

Whether the guest-starring celebs voiced yellow versions of themselves (a la Justin Bieber and Lady Gaga) or decided to lend their voices to other characters (like Michael Jackson and Lea Michele), we've rounded up some of the best pop star moments from the iconic series. Check out the photo gallery above to see the best of the best pop stars cameos on The Simpsons.