Robert Chase was House's original diagnostic-team fellow who later became a surgeon. Played by Jesse Spencer, Chase joined the first diagnostic team at Princeton-Plainsboro alongside Foreman and Cameron.
Chase began the series as an Australian physician whose background and loyalties sometimes placed him at odds with House. Over time, he became more independent and developed a stronger clinical identity, while remaining one of the show's longest-serving doctors.
After House's first diagnostic team changed, Chase continued working at the hospital and eventually moved into surgery. His career progression is a major part of his character arc, distinguishing him from fellows who left the institution or pursued other specialties.
Foreman and Cameron are common mix-ups because they were also members of the original team. However, Chase is the original fellow specifically associated with the later transition to surgery.