A theory put forth by Eric Idle
in his recent book The Road to Mars
that every comedian can either be classified as a White Face
(that is, one attempting to maintain order against all odds) or a Red Nose
(one actively promulgating the chaos).
Famous White Faces include John Cleese and Peter Cook; famous Red Noses include Terry Jones and Robin Williams.
It does get tricky, though...
"Steve Martin called me the other day, and said he finally got it. He was a Red Nose masquerading as a White Face, which I thought was a very interesting twist on it.... That's why Steve Martin is so confusing, because on the face of it, he looks like a White Face but he is in fact lovable. So that's why I think he tends to go Red Nosing."