The Dark Lord himself, Satan is a character whose path has collided with those of Beaver and Steve on many occasions.
Although Steve seemed reluctant to give back his new trident and position, it appears the roles were back to normal (or as "normal" it can get in this unfeasible realm) as Satan appeared next in Comic 101. He remembered having seen Steve before, but was quickly shushed to prevent any attempts of establishing continuity.
In the guest-made (semi-canon) Comic 122, he was seen as making soup with Beaver and Steve, but using a little too much fire and brimstone as Steve was running around on fire. Satan seemed a little sensitive about his cooking skills when Beaver pointed that out, though.
His next appearance was on Comic 139, as he guarded (or was just hanging out near) the Gateway to Hell that was found in the basement of the burger restaurant where Beaver and Steve worked for a short period. Beaver believed the gateway was one of the several reasons contributing to the restaurant being the centre of all evil in the universe.
He tends to start his opening sentences with "RAR!"