Captain Hopper was the commander of the ship which transported Professor Parry's expedition to Telos in the 25th century. He helped the Second Doctor defeat the Telosian Cybermen. He was one of the few survivors of the expedition.
He was angry that one of his men died trying to open the tomb doors and was suspicious of the Second Doctor and his companions. When the expedition opened the doors of the tomb and entered, Hopper and his men went to their ship to wait. They discovered that the ship had been sabotaged - the fuel pumps - and refused to let the expedition stay in the ship while it was being repaired.
When the expedition was trapped in the cavern, Victoria Waterfield fetched Hopper and Jim Callum to help. He and Callum opened the hatch to the cavern, and he went down through the hatch with smoke bombs. He helped the others back up the hatch. When the repairs to his ship were finished, he was able to fly the surviving members of the expedition off Telos. (TV: The Tomb of the Cybermen)