From Muppet Wiki

The Fat Blue Anything Muppet is an overweight, round-headed, blue rod puppet.

The name Fat Blue has often been used to refer specifically to Mr. Johnson, Grover's recurring customer in several skits. "Fat Blue" is also the only pattern to be identified in CTW style guides with an adjective as well as a color.

Examples of the Sesame Street characters developed from the Fat Blue Anything Muppet are listed below.

A blank Fat Blue	A blue duck	A blue fish	A blue rabbit
A blue spider	The Banana King	Ben	Bennett Snerf (monster form)
Big Jeffy	Clumsy Dwarf (Dwarf #1)	Didi O'Day and the Dew Drops singer	Dr. Livingstone
Evil Prime Minister	Fairy Godmother (Sesame Street)	"Fat Cat Scat" Performer	"Five People in My Family" Father
George Washington's Father	Gilbert & Sullivan	The Gonk	Grandmother Happy
Hard Head Henry Harris	Harvey Kneeslapper's victim	J Friends	John-Boy
King Peter the Persnickety	Lady Agatha	"Lefty" (no relation)	Lefty's boss
Little Chrissy	Miss Marble	Mr. Johnson	Mrs. Dogooder
Newsboy	The Old Woman Who Lives in a Shoe	Pokey the Dwarf	Professor Hastings
Simon Soundman	The Smartest Person in the Kingdom	Stella	A Tarnish Brother
Thomas Twiddlebug	Uncle Louie (Anything Muppet)

A live hand variant also exists, but has been used less frequently.

Captain Donald Cragen Muppet	Mama Countess	Ferlinghetti Donizetti	Grand High Triangle Lover
Joe Hundred Guy's Butler	King Goodheart