Wikipedia continues to not disappoint:

The name ‘hellbender’ probably comes from the animal’s odd look. One theory claims the hellbender was named by settlers who thought “it was a creature from hell where it’s bent on returning.” Another rendition says the undulating skin of a hellbender reminded observers of “horrible tortures of the infernal regions.” In reality, it’s a harmless aquatic salamander.

And this:

Other vernacular names include snot otter, lasagna lizard, devil dog, mud-devil, mud dog, water dog, grampus, Allegheny alligator, and leverian water newt.

Lots of fabulous nicknames there.