The Star Wars legend joined pal Burt Lancaster to film pilots for the show in 1969, teaching tots how to count and recite the alphabet, but he was sure the then-groundbreaking format would fail to entice young viewers to learn with Jim Henson's Muppets.
He tells the New York Post, "It was Burt Lancaster and I. He had the letters, and I had the numbers, or vice versa. I said to one of the producers, 'You know, this is not gonna work. The Muppets are just too scary for kids.'"
Sesame Street has since become the most widely-viewed children's TV show in the world and celebrated its 40th anniversary in 2009.