Clark was a clinic patient in the Season 1 episode The Socratic Method. He was portrayed by actor David Vegh.
Clark comes to the clinic complaining about hiccups and is seen by Dr. House. He says he has been unable to get rid of them, but says he has heard of something that will work and asks Dr. House to try it.
Instead, Dr. House walks out of the exam room and tells the nurse to mark the patient's chart as drug seeking behavior - the patient had asked for digital anal stimulation.