Who is Mustrum Ridcully from The Last Continent: A Discworld Novel and what is their importance?

A recurrent character in Terry Pratchett's Discworld novels, Ridcully is Archchancellor of Unseen University (UU) in Ankh-Morpork on Discworld. He is an abrasive character in his seventies, who greatly annoys the Dean and the Bursar, former classmates, whom he narrowly edges out for the top office long ago. To his credit, Ridcully has done away with the traditional means of job advancement—assassination. He brags of having an open-door policy but arranges never to be in his office. He is a master of illogic and nearly impossible to convince of the reality to which facts point. He tries not to understand anything that someone else could do for him. He makes tasteless jokes.