Frank

Frank is the security guard at the building where James works. 
Though there are many security staff, Frank is always the one on shift when James is working, and therefore, the biggest practical obstacle to dungeon operations. 
He is a fifty-year old with gray hair, a goatee that never goes out of style, and a little more muscle than would be expected on his wiry frame. 
James thinks of him as someone who values silence, and that he is the kind of person who felt like anyone trying to get away with anything was doing so at his expense - but that he could let anything slide as long as he thought he was in on the con.
Theodora thinks/thought that he is making fun of her and that he is a bad security guard.
Frank has a very mercenary attitude, and is currently being bribed several thousand dollars a month by James and company to look the other way from their weirdness. 
James meets him in chapter 24 and sets up their arrangement. He asks him if they're stealing from the office or if they're hurting anyone, and when James says no, he asks how much he's being bribed. He asks James if he's involved in something dangerous, but when James says yes, he doesn't ask any further. 
His attitude seems to be that, as long as he's in the loop, and they're not harming his job, he doesn't care what they might be doing. This makes Frank an awful security guard, but a good asset to the team.
Frank plays Hearthstone. He drinks his coffee black and his whisky on ice.
He is also in prison.