The Dominie

The Professor was an individual who travelled with Ace in the Cosmos. (PROSE: Republica)

Behind the scenes
The Professor was one of the two titular protagonists of The Time Travellers, one of the two subseries of BBV Productions' Audio Adventures in Time & Space. Portrayed by Sylvester McCoy, he was strongly implied to be the Seventh Doctor. Various people involved, including McCoy, felt they were too blatant a copy of Doctor Who and the BBC would send a legal warning over it. The second series of audios would rename him the Dominie, a suggestion by McCoy himself (Scottish for "teacher or master", according to Nigel Fairs). (REF: Downtime – The Lost Years of Doctor Who)

The 2021 novelisation of Republica (the first Time Travellers) tied itself to the licensed DWU via the licensed usage of Doctor X. It notably presented an alternative possibility for the Professor's identity instead of the BBC Doctor: near the end of the novelisation, the Professor say they need to get "back to the Cosmos, the spacecraft of Doctor Omega.