From Today In Science History:
In 1953, the 40-year-long hoax of the Piltdown Man ended when the British Museum revealed that it was a "perfectly executed and carefully prepared fraud." The Piltdown forgery was conceived, planned and executed sometime between 1907 and 1911. The faux hominid skull was constructed from the remains of a recent human cranium, later shown to have been thickened by disease during the subject's lifetime (thus giving the primitive look); half the lower jaw of an orangutan from which telltale parts had been removed and whose teeth had been filed to resemble worn human teeth; and a doctored canine tooth, probably from the same lower jaw. In all, thirty-seven pieces of bone and stone were involved, each carefully selected, each altered and stained.
Info on who did it is HERE.
Cartoon by Fredrick Burr Opper.