- You may be looking for the Time Lord of the same name.
Damon was an Atlantean surgeon and a protégé of Professor Zaroff. He performed operations that converted people into fish people. He almost operated on Polly. He later helped in the search for the escaped Polly and the Second Doctor and informed Thous that the fish people were revolting.
After the Doctor flooded the lower levels of Atlantis and the Atlanteans escaped to the surface, Damon tended to a wounded Thous. Damon was adamant that the new Atlantis would not have any "temples and priests and superstition". (TV: The Underwater Menace)