Basically, Undertaker was a Shinigami at one point in time and then he retired to go hang out in London with dead people. When he’s not digging graves, he still helps out and re-shelves stuff in the Shinigami Library. Granted, he’s pretty terrible at remember to re-shelve the crap he checks out.

Anyway, now he works, oh so originally, as an undertaker. It would hardly be important if he didn’t manage to be in charge of the bodies of people that get killed by weird supernatural things. This weird market that he has the monopoly on gives him enough information to act as an informant to Ciel. As long as he gets his payment of choice, that is. His payment of choice being, weirdly, laughter. I guess if I worked with dead people all the time, I’d need something to snicker at too.