First Doctor's emergency evacuation of the Council of Earth and Mars mission to Corbo, Chertzog was a companion of the First Doctor. He travelled alongside Dr Harroll Strong, and Strong's children, Jack and Dot, as well as Shelly and Hill. (PROSE: The Playthings of Fo)
Behind the scenes
Though a member of the Earth-Mars mission to Corbo, Chertzog is not actually introduced or mentioned until The Playthings of Fo.