Rap Master Squirrel is, as the name implies, a rapping squirrel. Introduced by a voice-over announcer, he suddenly appears in the Park in Episode 3427 of Sesame Street. He performs a rap about picking up litter, which is in fact the song "Litter Rap." Footage from that insert is intercut with the rapping squirrel at a stump and Big Bird and the kids cleaning up the park.
Since the squirrel follows in the traditions of both Jim Henson and Milli Vanilli by lipsynching, his voice is the same as that of the "Litter Rap" singer.