Keith Moon was an incurable drug addict who may or may not have been
mentally insane. He was a massive
prankster, and he had an incredibly unhealthy obsession with explosives, destruction, and destruction involving explosives. Everywhere he went, he got himself and his fellow
bandmates in big trouble with his antics, to the point that they
racked up a massive debt and almost went bankrupt.
During one concert, he had to be replaced because he kept passing out, thanks to his drug abuse. On several other occasions, his insatiable desire for destruction got himself injured quite badly, and he had to be repeatedly "rescued" by his bandmates or whoever happened to find him, who were none too happy to help him, knowing that he always invoked it upon himself. He ultimately died in 1978 at the age of 32, as a result of his incredibly self-destructive lifestyle. But when he died, his bandmates thought it was a prank; he was THAT much of a prankster. They didn't even realize it was legit until they went to his funeral and saw his mother weeping next to his coffin.