Lloyd Morrisett, the co-creator of the beloved children’s TV show Sesame Street, has died, the Sesame Workshop announced on Monday. He was 93.

He died of natural causes on Sunday at his home in San Diego, his daughter Julie told The Hollywood Reporter.

In 1966, Morrisett teamed with friend Joan Ganz Cooney to develop a program that could help prepare children for early schooling. Three years later, Sesame Street debuted, teaching kids how to read and count with the help of Big Bird, the Cookie Monster, Oscar the Grouch and the Muppets created by legendary puppeteer Jim Henson.

“Without Lloyd Morrisett, there would be no Sesame Street,” Cooney wrote in tweet accompanying Sesame Workshop’s announcement. “It was he who first came up with the notion of using television to teach preschoolers basic skills, such as letters and numbers. He was a trusted partner and loyal friend to me for over fifty years, and he will be sorely missed.”

The show would also go on to teach children about tolerance, divorce and racism. Its setting and cast was designed to be a welcoming mirror for underprivileged children, reflecting the diversity of urban areas such as New York City. Amid the backdrop of the civil rights movement of the 1960s, it was among the first TV shows to show Black and white children playing together.

“It was an urban environment, designed from the beginning to show diversity,” Morrisett said in a 2019 interview with American University Radio as the show was celebrating its 50th anniversary. “And, of course, the Muppets were different colors, different shapes, different sizes. And, that was purposely put in to show kids that they could be friends with people who weren’t like them.”

Morrisett served as the chairman of the board of trustees for Sesame Workshop, which oversees Sesame Street from 1968 until 2000, before being named a Lifetime Honorary Trustee. 

“A wise, thoughtful and above all kind leader of the Workshop for decades, Lloyd was fascinated by the power of technology and constantly thinking about new ways it could be used to educate,” the Sesame Workshop said in a statement on Twitter.

The show he helped create became one of the longest-running shows in the world, attracting millions of viewers each week in more than 150 countries. Over its five-plus-decade run, Sesame Street has won 216 Emmys and 11 Grammys, and in 2019, it became the first TV program to receive the Kennedy Center Honors.

Morrisett and Cooney accepted the recognition, accompanied by Big Bird, Elmo and Abby Cadabby.