Professor Sondergaard was an Earth Empire scientist. He was forced by the Marshal of Solos to flee to Solos, where he studied the Solonians, trying to find a cure for their "mutations". With the Third Doctor's help, he discovered that the changes were actually part of their natural life cycle. After the Marshal's death he decided to stay on Solos with Ky to help the Solonians fulfil their destiny. (TV: The Mutants)