Harry Sullivan, portrayed by Ian Marter, traveled with the Doctor between Robot and Terror of the Zygons and The Android Invasion.
Surgeon Lieutenant Harry Sullivan was assigned by the Brigadier to look after the newly-regenerated Doctor, and soon accepted an invitation to enter the TARDIS.
Unflinchingly brave, yet clumsy, Harry was of invaluable assistance during a brief series of adventures, which included a visit to Skaro to witness the creation of the Daleks and an encounter with the Cybermen.
Harry returned to Earth when the Doctor was summoned by the Brigadier to investigate a series of disappearing oil rigs, and decided to stay when the Zygon menace was thwarted. The Doctor and Sarah later encountered an android replica of Harry, created by the Kraals.