Phrenology was a discredited science that used to be quite popular, whereby the shape and size of a person's skull was supposed to indicate their character and mental abilities. After he died in 1809, phrenologists stole the famous Austrian composer Haydn's head.
They hoped to test their theories that head shape determines abilities, supposing that the head of such a musical genius would confirm their work and lend them credibility. However, when Haydn's family refused to turn over the head, the men robbed his grave, chopping off the cranium and absconding with it.
Once the family learned of the theft, they naturally insisted upon its return. So the phrenologists gave them a different skull instead, which the family soon discovered to be that of a woman. The family was understandably upset, and insisted upon the real skull's return.
So the grave robbers then gave them a different skull, this time of a man near the same age as the deceased composer, but still not Haydn's. The family was convinced, and had the skull re-interred. Meanwhile, the real skull was studied and eventually used as a garden ornament, until it came into the possession of a music appreciation society many years later.
Finally in the 1950s, Haydn's skull was returned and joined the rest of his body in its final resting place. The phony skull was never removed though, out of respect for the unknown man.