Vice-Chancellor
This is a title and post mentioned in Equal Rites, but presumably in abeyance since Mustrum Ridcully became Archchancellor at Unseen University, as he is certainly all the leadership you'll ever need...
The last named Vice-Chancellor was Profesor Treatle, in Equal Rites, who brought Simon to UU and who was presumed killed in the war of the Sourceror.
Recent talk in Unseen Academicals suggests that after the departure of the Dean, this office has now devolved on Ponder Stibbons, as most vacant offices at the Univerrsity tend to do. Well, the only other Faculty member with anything like the same gravitational pull for vacant titles is Rincewind, and Ridcully is in all probability determined to avoid this, preferring Ponder as the most sensible wizard for miles around.