Dr Undershaft was the chorus director at the Ankh-Morpork Opera House. A rare bird, he seemed to believe that what mattered in a singer was their voice, not their sparkle or looks. Obviously this kind of idiosyncratic quirk marked him out to the Opera Ghost. Not long after nearly dying of pleasure at hearing Agnes Nitt sing the famous Departure aria perfectly, he really dies when he stumbles upon the Ghost smashing up instruments. The Ghost doesn't take kindly to the interruption, so strings him up. Strings - geddit?
He is followed as director by Walter Plinge.