Heinz Karl "Nali" Gruber (b. 1943), who styles himself HK Gruber professionally, is an Austrian composer, conductor, double bass player and singer. He has composed music for Yo-Yo Ma and Håkan Hardenberger.
Gruber appeared in The Ghost of Faffner Hall episode "Reacting to Sounds". During Fughetta Faffner’s half century sound check of Faffner Hall, Fughetta hears a few ghostly sounds and finds a symphony orchestra under the direction of Heinz Karl Gruber in one of the rooms.