United Kingdom, May 23 -- 'Seinfeld' actor Michael Richards says his infamous racist tirade was sparked by a heckler telling him he wasn't funny.

The 74-year-old, who made a fortune and was skyrocketed to global fame playing Kramer on the hit comedy sitcom, saw his career and reputation left it tatters after he was filmed unleashing a tirade of racial slurs during a stand-up show in 2006 at the Laughter Factory in Los Angeles.

He has now told in his upcoming memoir 'Entrances and Exits' about the incident that he was hurting from the failure of his post-'Seinfeld' sitcom 'The Michael Richards Show' - which lasted only eight episodes in 2000 - at the time of the gig, even though six years had passed since it was axed.

Michael says he he...