Elmo is a red Muppet from the popular PBS children's television show, Sesame Street. He made his official debut on the show in 1985, and has been a regular on the show since 1986 (his popularity increased starting in the early 1990s, and is now one of the most popular characters on the show today).
He was once sent to Ronald Reagan Reeducation Center for going to the wrong fundraiser, where he hanged himself.
On The Simpsons, Elmo is usually voiced by Nancy Cartwright. However, on Sesame Street, he was voiced by Kevin Clash. Kevin resigned from Sesame Street in 2012 because of a scandal. Ryan Dillon now voices him.