Harvey is the secondary protagonist of the episode, It's a Wonderful Tiny Toons Christmas Special. He is a white rabbit who wears only a green shirt, a purple bow tie and khaki slacks. He is voiced by Dan Castellaneta.
In the episode, he takes on the role for Clarence Odbody (reviewing with the boss of the angels about Buster Bunny's career on "Tiny Toons", as Clarence reviewed George Bailey's life with Joseph, the head angel, in "It's a Wonderful Life"), except that he is much sillier. He grants Buster his wish of never existing on Tiny Toons so that Buster will realize how important he is before he exists again to take back control of the show with Babs. It is not revealed until the ending that "Harvey" is actually Bugs Bunny in disguise.
It's interesting to note where the name for the character of "Harvey" is actually derived. Harvey here is the equivalent of Clarence from It's A Wonderful Life, which starred Jimmy Stewart. Stewart also starred in a 1950 film titled Harvey, detailing the relationship between Stewart's character Elwood and a tall "invisible" rabbit who went by the name of "Harvey." Thus, the name being used in this Tiny Toons episode for the helpful "angel" rabbit character is no coincidence.