Kalikoff

Kalikoff is one of the "Sturmhalten sewer rats" assigned to guide Lars, Zeetha, and Da Boyz through the undercity. He's the one with hair, and who is barely taller than Krosp. He and his associate Sturvin have been working there for more than twenty-seven years, and know it well, apparently including the Deepdown (though they prefer not to go there lately- apparently it got more dangerous since twenty to twenty-five years ago, when it was fun.)

Of the two partners, Kalikoff was apparently the death trap specialist. This enabled him to save the rescue party's lives when he escaped a monster with his Official Sturmhalten Sewer Rat Knife and found the secret door into (and, more importantly, out of) the oubliette.

He managed to hold his own without too much more incident in the later confusion, and was airlifted out on the Circus' stolen airship. His current whereabouts are unknown, since it's not clear whether the invitation to England included him but it's certainly not yet safe to go back home yet.

Though his status as a revenant is not attested, he is from Sturmhalten...