Squelch was the undead zombie dog pet monster of Skud Derringer, while he lived in the Monastery of Uthgar deep in the mountains of Ssathra. It was adorable, and could be brought back to undead life by Skud should it ever "die". It was given to Skud by The Old Master, as a means of making him more chill and cool. It was then killed when The Skull Bandits raided and burned down the Monastery. It was then, presumably, brought back to a state of undead-ness by Skud, though this happened off-screen.
Between the dog's introduction, and the backstory of how Skud got it, it was forgotten about, so when the dog came back into the story no one remembered its name. This resulted in it, temporarily, being named Hambone, and then Spud. But we all remember its real name.