Qual'n'Gurtha is a green one-eyed octopus monster. In his own words, he is an "eater of worlds", "devourer of worlds" and "gourmand of galaxies". Beaver releases him from a behind a door which shouldn't be opened in Comic 159. Qual'n'Gurtha declares his intent to end our pitiful universe, starting, in Comic 160, with cakes baked by Steve - but (luckily) the cakes prove more filling than he expects.
Just two of his tentacles are visible in a filler strip (Comic 223).
Qual'n'Gurtha also appears in a guest strip (Comic 226) by Chris Yates. He attempts to buy a can of Dr Pepper, and Steve lends him a quarter. However, he must settle for a can of Pepsi instead - which he is unable to open, as he is poorly equipped for the task (having only tentacles).
In the guest strip, Qual'n'Gurtha is blue instead of green.