Wowbagger the Infinitely Prolonged is one of the universe's very few immortal beings from Douglas Adams' Hitchhiker's Guide to the Galaxy series. Unfortunately, Wowbagger does not have the instinctual ability to cope with immortality, as it was an unfortunate accident involving an irrational particle accelerator, a liquid lunch, and a pair of rubber bands that caused his immortality, the details of which have never been made entirely clear, which has resulted in a number of people looking very silly, or dead, or both, in attempts to replicate the event.

Eventually tiring of immortality, Wowbagger conceived his purpose: he would insult the universe and everybody in it. As a testament to his true immortality, he chose that in addition to insulting every last person, one by one, he would do so in alphabetical order.

Several million years ago (two by Ford Prefect's guess), Wowbagger landed on prehistoric earth and insulted Arthur Dent, calling him a jerk. Arthur's incredulity at seeing another being (after having been stranded on prehistoric earth for several years) led Wowbagger to confirm Dent's identity before repeating "You're a jerk, a complete kneebiter," before stranding him again.

Wowbagger was first featured in Life, the Universe and Everything, not The Hitchhiker's Guide to the Galaxy.