Martin Donaldson

 was a World War I veteran living in London in the 1920s.

Martin fought in World War I, consequently losing his leg in battle. After the conflict, he went to live with his sister, Kitty Donaldson.

In 1921, he met the Eighth Doctor and Liv Chenka when Kitty asked the Doctor to check up on him, thinking he was a medical doctor. This led the Doctor to investigate an unstable time field around Martin, but not before Martin had taken Liv on a tour of London, during which they went to see a Buster Keaton film, went to a restaurant and visited the British Museum.

All through this, Martin left items such as a diamond ring, and an alarm clock which aided the Doctor in evading capture by androids. When the androids took the TARDIS, he saved the Doctor, Liv and Kitty by jumping onto a temporal grenade. This caused him to become stuck in a time loop, reliving the events of the previous day, hence the reason for him leaving items to assist the Doctor and Liv. (AUDIO: A Life in the Day)

Personality
Martin Donaldson was brave and resourceful. He liked comedy films and enjoyed visiting the British Museum. As he tried to defuse the grenade with the Doctor, he confessed that he had fallen in love with Liv. (AUDIO: A Life in the Day)