Bowerick Wowbagger the Infinitely Prolonged became immortal after an accident with a few rubber bands and a particle accelerator. After years of total boredom, or possibly centuries, he decided to insult everyone in the entire universe in alphabetical order.
He appears at prehistoric Earth to insult Arthur Philip Dent, saying "You're a jerk, a complete kneebiter." He later appears at Lords Cricket Ground to insult the dying Arthur Philip Dent, calling him a "no-good dumbo nothing." He also shows up on Krikkit to insult Arthur Philip Dent, but, before insulting him there, he consults his clipboard and asks, "Hey, haven't I done you before?"
In the radio show, he finally insults the Great Prophet Zarquon, who kills him, ending Wowbagger's eternal suffering.
In the sixth book Wowbagger insults gods to get them to kill him. He partially succeed when Thor hits him so hard that he loses his immortality. After that, he lives happily ever after (well, not quite ever after) with Trillian.