Harding Wellman

 was a mountaineer who was killed in an avalanche while climbing the Swiss Alps in 1913. He was commemorated in the Tremayne School chapel in Switzerland.

When the Fifth Doctor conducted a séance on 22 December 1963, he manifested as a physical being. He had epileptic fits which caused the poltergeist activity in the school. (AUDIO: Winter for the Adept)