Chronotis

Salyavin was a Time Lord who was sentenced to be held on Shada, the Time Lord's prison planet.

Salyavin had amazing mental powers, and was able to "move his mind into another's", but was also able to make the Time Lords forget about Shada, partly by stealing The Worshipful and Ancient Law of Gallifrey.

As Chronotis
Salyavin hid for a great many years at St. Cedd's College in Cambridge, on Earth, living in his TARDIS (which was an earlier model than the Type 40).

When Salyavin began approaching his 13th life he sent a message to the Doctor to come and see him, so he could return The Worshipful and Ancient Law of Gallifrey, which he had stolen. However, it was not until the Doctor's eighth incarnation that he was able to follow up his request. (DW: Shada, WC: Shada)

He died when Skagra's sphere attacked him searching for information concerning The Worshipful and Ancient Law of Gallifrey, however due to a serendipitous mistake by Clare Keightley with Salyavin's TARDIS he was brought back into existence.

Professor Daniel Joyce

 * It is suggested in various readings the Joyce is Salyavin

Professor Daniel Joyce was a professor at Berkley, the Eighth Doctor sought his assistance while in San Francisco. (EDA: Unnatural History)