“House” is the nickname commonly used for House M.D.'s original diagnostic team leader, Dr. Gregory House.
Colleagues almost always address him by his surname rather than Gregory. This convention reflects medical workplace formality and the character's preference for emotional distance. The title House M.D. itself uses that surname as the show's central identifier.
The original team includes Foreman, Chase and Cameron, who call their supervisor House in case discussions and hospital scenes. “Greg” appears occasionally in personal contexts, but it is not the dominant form of address. “Doctor House” is also heard, especially from patients or staff.
Because the question asks for the nickname used in the series, the canonical short answer is House—not Hugh Laurie, the actor, or Gregory, the character's first name.