The Hitch Hikers Guide to the Galaxy/ZarquonIronic, since Adams was an atheist. (Why is this ironic? Adams refered to babel fish and Vogon poetry too, but probably didn't believe in them, either.) Then again, Zarquon is mentioned by Adams in a trademark sarcastic way, referring to the (almost) failed "Second Coming" of said prophet.
Zarquon's second coming does actually occur - at the Restaurant at the End of the Universe. Since the said restaurant occurs an infinite number of times at the end of the universe, due to a specially created time-loop, Zarquon's impossible appearance at the restaurant became finitely improbable, and therefore happens just before the universe ends.
The second coming is not particulary spectacular, and Zarquon turns out to be a rather feeble old man, who had '..had a lot of things to do.'
'Holy Zarquon's Singing Fish' is an expletive phrase used, but not explained, by Zaphod Beeblebrox when he faces extreme danger.