Stephen is a repairman who was called to install the control boxes in the Bates house after the furnace broke. He warned Norma against lighting the furnace as it would cause a gas leak and offered to have it taken away. As he left, she introduced him to Norman, who had eavesdropped on the conversation from the top of the stairs. (Unfaithful)
After Norma died, Romero paid Stephen a visit at his store and asked if he had looked at the faulty furnace. He also asked if Norman had overheard his conversation with Norma and even though Stephen refused to give any information, Romero grabbed him and threatened him before Stephen finally admitted that he had met Norman. (Norman)