Magister1971

A seller using the username Magister1971 once sold Giles a fake DVD of a missing Doctor X episode. The DVD knocked out PROBE's technology, allowing a Nolvox control node to be stolen from the Dr Smith Shelf. (WC: Case File - Doctor X)

Behind the scenes

 * As "Magister" is the Latin term for "Master", the suggestion is that this individual was the Master. He could further be narrowed down to, who debuted on television in 1971. However, this was not explicit because Case File - Doctor X was not licensed to us the Master.