Dr. Brock Sterling is a character on the "show within a show" Prescription Passion. "Dr. Brock" is played by in-universe character Evan Greer, who is in real life portrayed by the actor Jason Lewis.
The "Dr. Brock Sterling" character can be seen in the episodes No More Mr. Nice Guy (when House watches Prescription Passion during a break) and Living The Dream when House and the team watch episodes of the show looking for clues to find the reason "Evan Greer" is ill.
Unlike the "actor" who plays him (who is a healthy eating teetotaller who is looking for a committed relationship before getting intimate), Dr. Brock is a womanizing alcoholic surgeon who is not above sleeping with, and impregnating, his own fiancée's sister. Dr. Brock prefers to drink gin and tonic, but regularly drinks straight out of the bottle, particularly when trying to steady his hands before surgery. The major plot point of Prescription Passion that Gregory House wants to know about is who is the father of the twins one of the females is carrying. "Greer" tells House that only one of the twins is his.