S3, E17: When Jonathan acts strangely, Clark believes that his Kryptonian father, Jor-El (voice of TERENCE STAMP - "Superman II"), is sending Jonathan messages and is the cause for his father's withdrawal from the family. Clark goes down to the caves to confront his biological father, but Lionel finds Clark there and begins putting the pieces together--leading him straight to reclusive scientist Dr. Virgil Swann (recurring guest star CHRISTOPHER REEVE), who knows Clark's origins. As the two billionaires face off, a deal is struck, and Lionel's true motives are revealed.