From Muppet Wiki

B.B. King (b. 1925) is a well-known blues guitarist and songwriter.

King said the alphabet on Sesame Street in Episode 0130.

He returned in Season 32 (2001), performing a song about the letter B with Bert, Benny Rabbit, Big Bird and Baby Bear. (EKA: Episode 3962)

He appeared in "Yakety Yak- Take It Back", a recycling PSA that eventually aired on Sesame Street.