The Bursar

[close] The Bursar, real name Dr. A. A. Dinwiddie, (spelled with an "O,") D.M.(7th), D.Thau., B.Occ., M.Coll., B.F., is an "idiot savant," who has been sadly unsettled by his work at the Unseen University. When he first appeared in Eric and Moving Pictures the Bursar actually appeared relatively sane, but during the events of Reaper Man he became increasingly unhinged. As a consequence he requires regular ingestion of dried frog pills to maintain normality, though he is essentially overdosed until his mind is in a heaven of pink clouds and his body is stiff. As he could still apparently function as a bursar - a job no-one else wanted - it was initially a minor consequence to his fellow wizards.
When there is a threatening situation, the Bursar tries to contribute to the discussion, but his contributions are rarely relevant. Sometimes he speaks as though he's doing something else, e.g. calling for a pub landlord while he's really at a college council meeting. Sometimes he talks as though he has imaginary alternate personalities. Sometimes his sayings are entirely incoherent. On at least one occasion, the Bursar went through the previous day... backwards. Also, he has hallucinated that he could fly at least once, which led to Ridcully trying to get him away from the ceiling. His insanity is so renowned, that "going bursar" has become a byword for "going crazy" in Ankh-Morpork.
The Bursar's original personality could be considered quiet and reserved, and he became the UU Bursar because no-other wizard was so happy as he could be when working with numbers. However, Mustrum Ridcully's promotion to Archancellor led to the Bursar's current insanity, as Ridcully's personality wore away at his own, and he had eventually reached his current-level of (in)sanity. The Bursar's idea of excitement was originally a soft-boiled egg, and Ridcully's presence made him highly strung and nervous. Nowadays there are many kinds of "health restrictions" for him, like only using a wooden spoon at meals, and not eating anything sugary.
Happily, just very recently, the Bursar's colleagues had figured out that they could make the Bursar hallucinate that he's sane, (since events in The Truth,) which most of the population already do without the help of dried frog pills. The Bursar now acts rational and coherent except that he really does fly around, and that it's still relatively easy to upset him.
Like many members of the faculty and college council, the Bursar is usually referred to by his job-title rather by his name, (the only other members of the faculty to be named are Rincewind, Mustrum Ridcully, Ponder Stibbons, Horace and Henry.) Dr. Dinwiddie's first definite appearance is in Moving Pictures. He may also have been the Bursar in Eric, since it is not a post that wizards kill the incumbent to attain.
As of Unseen Academicals, it seems that his insanity has reached the point where he could not properly fulfil his duties. He is said to have developed a specialised form of dyslexia, where he is unsure as to where the decimal point goes. Perhaps his increasing addiction to the sort of higher mathematics which can only be understood by three other people as well as those who habitually write in crayon, dribble a lot, and require serious medication, has rendered him unfit for the more mundane sort of number-juggling. His role as Bursar has since been taken on by the increasingly-overburdened Ponder Stibbons.