Chertzog

Chertzog was a tough, middle-aged Dutchman who briefly travelled with the First Doctor.

Biography
Chertzog, along with Hill, Shelly, and Harroll Strong and his two children were part of an exploratory mission by the Council of Earth and Mars to the planet Corbo when they were captured by Ulla, who thought they were Lohk's spies. The First Doctor met the children and helped free the four men from Ulla, before hastily ushering the six of them into his TARDIS to take them home to Earth. (PROSE: The Playthings of Fo)

Instead of them arriving on Earth, they landed on Rhoos and Chertzog became a temporary companion of the First Doctor. After exploring the planet and liberating its denizens from the clutches of the Cyclops Fo, the Doctor once again set about trying to take them all to Earth. (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.