Captain Kangaroo was canceled in 1984 after 29 seasons, and
Great Space Coaster ended, freeing up Clash to work on projects with Henson such as the film
Labyrinth and
Sesame Street. Clash started working at
Sesame Street for ten episodes in 1983, mostly performing nondescript, stand-in puppets known as
Anything Muppets. Some of his earliest characters included the
saxophone-playing
Hoots the Owl (based on
Louis Armstrong), the infant Baby Natasha, and inventor Dr. Nobel Price. He worked on the 1985 feature film
Follow That Bird. After 1985,
Elmo, a furry red monster, became his main character. Three puppeteers, including
Richard Hunt, had performed Elmo previously, but it was Clash's development, with a falsetto voice, that established the character. He based Elmo's character on the preschool children that attended his mother's daycare in Baltimore and upon his own personality and the personality of his parents. Clash followed the advice of fellow puppeteer
Frank Oz, who told Clash to always "find one special hook" for each character. Clash decided that the central characteristic for Elmo should be that he "should represent love". at the
Peabody Awards in 2010 After the height of Elmo's popularity, especially the "
Tickle Me Elmo" craze in 1996, Clash's responsibilities at
Sesame Street increased. He recruited, auditioned, and trained its puppeteers, and became the senior Muppet coordinator, a writer, director, and co-producer of the "
Elmo's World" segment of the show. He found working with the co-productions "a lot of fun" and "very rewarding". In 2007, he was promoted to senior creative adviser for the Sesame Workshop. Until 2011, he was the sole performer as Elmo in all his public relations appearances, making his schedule, as he called it, "crazy". Cheryl Henson, president of the Jim Henson Foundation, called him "essential" to the show. Clash worked on the first film version of
Teenage Mutant Ninja Turtles in 1990 and the sequel,
Teenage Mutant Ninja Turtles II: The Secret of the Ooze, which was dedicated to Henson, in 1991, voicing
Master Splinter. He performed in several productions with
Jim Henson Productions, including as the Muppet Clifford in
The Jim Henson Hour (1989), and performing the puppetry for Frank Oz's characters (
Miss Piggy,
Fozzie Bear,
Sam the Eagle, and
Animal) in
Muppet Treasure Island (1996). Clash performed in the films
Muppets from Space (1999) and ''
The Muppets' Wizard of Oz (2005), and the TV series Muppets Tonight'' (1996–1998), in which he reprised Clifford, who served as the show's host. He performed characters and worked behind the scenes on the sitcom
Dinosaurs. In 2006, Clash published his autobiography, co-written by Gary Brozek and Louis Henry Mitchell, entitled
My Life as a Furry Red Monster: What Being Elmo Has Taught Me About Life, Love and Laughing Out Loud. After a hiatus of several years, Clash returned to performing with the film
The Happytime Murders (2018), directed by
Brian Henson and co-produced through
Henson Alternative. He later puppeteered in the 2019
Netflix series
The Dark Crystal: Age of Resistance, which serves as a prequel series to the 1982 Jim Henson film
The Dark Crystal. ==Personal life==