When the Tanngrisnir rescued the Heart of Gold, which had in turn rescued Arthur Dent, Trillian Astra, Ford Prefect and Random Frequent-Flyer Dent from the Grebulan multi-dimensional assault on Earth, he met and fell in love with Trillian, a woman with whom he would wish to grow old. He also met Zaphod Beeblebrox and insulted him, calling the fugitive ex-President a "steatopygic moron". When Zaphod demanded to know what steatopygic meant and was informed it meant "fat-arsed", Zaphod threatened to kill Wowbagger. Wowbagger informed Zaphod that he, Wowbagger, was immortal, the ex-President revealed that he was friends with Thor, "another immortal" who could kill Wowbagger with Mjölnir, Thor's Uru hammer. Wowbagger took him at his word and allowed Zaphod to return to the Heart of Gold in order to travel to Asgard, home planet of the Æsir.

Upon arriving at the planet Nano, they discovered that the Heart of Gold had arrived there first. Zaphod had succeeded in persuading Thor to try and kill Wowbagger. Thor didn't kill him outright, but managed to hit him so hard that he lost his immortality, whereupon Thor decided that since Wowbagger was no longer immortal, the fight was no longer a fair match and refused to finish him off. After that, Wowbagger accepted Trillian's poroposal and decided to live happily ever after with Trillian.

Wowbagger was not the first immortal in his family, but was the distant descendant of Wowbagger Ultrajax who had become artificially immortal, although he did it by stealing the Quentulous Stone of Firefram, which made the holder immortal, from the Lajestic Vantrashell of Lob.