The Visitor

 was a Time Lord. He was a member of the Celestial Intervention Agency who questioned Jamie McCrimmon about his involvement in the Glorious Revolution in 1688 after restoring his memories of his travels with the Second Doctor.

He later offered Jamie the opportunity to keep his memories. However, Jamie chose to once again forget as he and his wife McLaren had a good life together, which he did not think would have possible if he knew all that he had lost. (AUDIO: The Glorious Revolution)

Behind the scenes
The true name of this Time Lord is not known, so he is known as a visitor to Jamie.