Usually a white man, but sometimes a white woman, who is too stupid and classless to solve a problem - and their dilemma is usually solved by a black woman or sometimes a black man who is far more intelligent and/or stylish than the white schnook in question.
My wife cracks up whenever I see one of these advertisements come on, because I inevitably say: "Aaarghh! I can't stand these stupid white people! Where can I buy this product?"
The IBM commercials are notorious for this.