Harold Lam is House's primary rival in the annual Greater Schenectady Chili Cook-Off and Spud Gun Tournament's spud gun competition. He appears for the first time in The Dig although it is clear that he and House have known each other for years. He is portrayed by actor Justin Chon.
In the previous four years of the tournament prior to The Dig, Harold has finished first all four times and Gregory House has finished as runner-up. House is determined to beat Harold and enlists the involuntary help of Thirteen after her release from prison because of her expertise in controlled combustion. Knowing that the competition is weighted equally for distance, hang time and accuracy, they decide to go for pure power.
When they arrive at the festival, Harold is there as well with his new gun, which is much bigger than House's and is also built for pure power. He and House exchange fake pleasantries. When House tries to intimidate Harold, Harold realizes at every step that House is lying. It's not obvious what Harold does for a living, but he's obviously very bright. He says he interned at the Jet Propulsion Laboratory, which probably means he is a post-doctoral fellow or something similar. He appears to be in his late twenties.
Harold is well known to House as a serial harasser of any good looking woman, especially women connected to House. He warns Thirteen about Harold in this regard.
After Thirteen breaks the news to House about why she was in prison, Harold senses some separation between the two and comes by to gloat and say he's going to take a chance on Thirteen. The last we see of Harold is when House points his spud gun at him and Harold incredulously says "You wouldn't!".
Luckily for House, Harold had made a clumsy pass at the Sheriff's daughter the night before. As a result, the police let House off with a warning for shooting Harold. However, House was obviously disqualified from the competition.