Jascha Heifetz

From Muppet Wiki

Jascha Heifetz (1902-1987) was a noted musician mentioned in episode 210 of The Muppet Show. Rowlf the Dog refers to himself as "another Jascha Heifetz," although Heifetz was a violinist. Rowlf assures guest star George Burns that nobody will ever know the difference.

Rowlf uses the same joke on Kermit in a scene depicting their first meeting in The Muppet Movie. While playing piano: "I'm no Heifetz, but I get by."