Isaac Lee Hayes, Jr. (August 20, 1942 – August 10, 2008) was the voice of Chef from 1997 until he left South Park because of the controversy surrounding "Trapped in the Closet" in 2005. It is most likely that he left because of the episode's portrayal of Scientology; and, the fact that he was a Scientologist himself.
Well before leaving, Hayes made an appearance as himself in the mockumentary, Chef Aid: Behind the Menu, in which he did not know who Chef was.
In a 2007 interview, Hayes mentioned he quit because "They (Parker and Stone) didn't pay me enough... They weren't that nice."
On August 10, 2008, Hayes passed away at the age of 65 due to complications caused by a stroke and was commemorated by South Park Studios.