Yes, that is a Sponge-Bob Squarepants hat that the birthday boy is wearing! How cool is that? And drinking a diet Coke -- I guess they broke out the cigars and champagne later.
An article purporting to be written by Cheetah, which will make you cringe and wince in shame at our species for having produced a writer capable of such incredible crap, yet containing some interesting information withal, is available here.
Cheeta's last role was in 1967's Dr. Doolittle, opposite Rex Harrison, where he played Chee-Chee. Actually, Cheetah was only a stage name: his real name is Jiggs.
In retirement, Cheetah lives at C.H.E.E.T.A., a primate sanctuary in Palm Springs, where he's embarked on a second career as a painter! Check this out!