Clastivas

Clastivas was a TARDIS mechanic.

Maris questioned him over the First Doctor's theft of a Type 40 TARDIS after she'd been hired by his first TARDIS to find out what had happened to him. At the time of the questioning, Clastivas was working on the console of a Type 58 TARDIS.

Clastivas had asked around about the Doctor, and he told Maris the Doctor had no need to steal a TARDIS at all. (PROSE: Celestial Intervention - A Gallifreyan Noir)