Sesame Street‘ co-creator Lloyd Morrisett has died, Sesame Workshop announced on Monday. He was 93 years old.

“A Lifetime Honorary Trustee, Lloyd leaves an outsized and indelible legacy among generations of children the world over, with ‘Sesame Street’ only the most visible tribute to a lifetime of good work and lasting impact,” Sesame Workshop (originally known as the Children’s Television Workshop) wrote of one of its founders.

Morrisett co-founded the Children’s Television Workshop with his close friend and fellow “Sesame Street” creator Joan Ganz Cooney in 1968, where he continued to serve as chairman of the workshop board until 2000. He remained a board member until he died.

Prompted in part by the Civil Rights Movement and the war on poverty, the duo set out to create a TV series that would give disadvantaged children a chance to prepare for school. Thus, they created “Sesame Street” in 1969. After famously spawning the hit children’s series, the Children’s Television Workshop was later renamed as Sesame Workshop.

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“Without Lloyd Morrisett, there would be no ‘Sesame Street.’ 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,” said Ganz Cooney of his passing.

“In co-creating ‘Sesame Street’ and other Children’s Television Workshop programming, Lloyd Morrisett not only gave start to some of the world’s most beloved — and most Emmy-awarded — television programs; he and Joan Ganz Cooney defined the gold standard for a whole genre of television,” said Adam Sharp, president and CEO of The National Academy of Television Arts & Sciences (NATAS), in a statement.

Sharp continued: “Today, the original ‘Sesame Street’ audience can share the delight of his creation with their own grandkids, who will undoubtedly share the experience with yet more generations as his impact long endures. Our Academy mourns his passing and knows that the love and warmth so ever-present in all his work is today being reflected back to his family by the millions of viewers whose lives he enriched.”

Additionally, Morrisett also served as president of The John and Mary R. Markle Foundation from 1969 to 1998, during which time he launched the foundation’s program in communications and information technology. Prior to joining the Markle Foundation, he served as vice president of the Carnegie Corporation of New York and the Carnegie Foundation for the Advancement of Teaching.

Born in 1929 in Oklahoma City, Morrisett received his B.A. at Oberlin College. He later became a trustee of the college and was named the board chairman from 1975 to 1981. He later did graduate work in Psychology at University of California at Los Angeles, and earned his Ph.D. in Experimental Psychology at Yale University.