Kronos Quartet is a string ensemble established in the 1970s with dozens of recordings released to date. When they appeared on Episode 2420 of Sesame Street in 1987, the members of the quartet consisted of David Harrington, John Sherba, Hank Dutt, and Joan Jeanrenaud.
In their episodic appearance, Big Bird meets the players in the yard. They explain to Big Bird how a string quartet works and how it's something like how they're communicating. (YouTube) In another segment, the players are kicking around a soccer ball with Big Bird. They show him how passing the ball to one another is something like how they practice playing music. (YouTube) They performed the Sesame Street Theme during the episode's credits.
David Harrington commented in 2012: