Tyler (The Three Doctors)

Dr Tyler (although the Doctor called him Professor Tyler at one point when frustrated with him) was a scientist who researched cosmic rays.

Biography
Tyler's monitoring device accidentally picked up one of Omega's Gell guards, which transported him to Omega's anti-matter universe. He began to talk to himself, and the Third Doctor and Jo Grant found him and the trio began to assess the situation, until they were captured by Omega's Gell guards.

Tyler, once inside Omega's lair, attempted to escape. Even though the Third Doctor advised against it, he tried to anyway, with little success. When Omega revealed himself, Jo and Tyler were put in a cell. When the Second Doctor, the Third Doctor and Sergeant Benton joined them both, Tyler couldn't quite believe that a world of antimatter existed, and got very excited about the prospect of singularity, but also got perplexed at the two Doctors. When the two Doctors managed to use their will to create a door in the wall, they left to see Omega, and told everyone to stay in the cell. They didn't, and Jo, Benton and Tyler came across some Gell guards, and as they tried to open the door, the Brigadier and Arthur Ollis managed to open the door from the other side as they were trying to get in.

After the crisis ended, Tyler was safely returned to Earth. (TV: The Three Doctors)