From Muppet Wiki

Jackie Robinson (1919-1972) was the first African-American Major League Baseball player. He played with the Brooklyn Dodgers from 1947 to 1956, and he was named the National League's Most Valuable Player in 1949.

Robinson recorded an insert for the first season of Sesame Street, saying the alphabet. Robinson's insert was included in a number of episodes, beginning with episode 0054.

The clip appeared on Old School: Volume 1.