Professor of Astrology
The Professor of Astrology was a wizard mentioned in The Light Fantastic. He was, along with most of the other wizards, unnerved by Trymon. Presumably he was a senior astrologer, as he reported to Trymon on behalf of the other astrologers working in Unseen University's observatory.
He reported to his new master that they had discovered what appeared to be a star, except that it was red and it was much, much bigger then Great A'Tuin and the Disc combined. And that Great A'Tuin was headed right for it, and they were going to hit it. Realizing that this was probably the disaster that the Octavo was needed for, Trymon ordered him to cast Rincewind's horoscope to find him. In the process, the Professor of Astrology discovered that Rincewind had been born under a bizarre collection of occult signs- he was born under The Small Boring Group of Faint Stars, and that the shadow of Cori Celesti during the time of his birth was apparently quite significant.
He was able to discover that Rincewind's horoscope boiled down to "Don't upset any druids", which pleased Trymon, who sent off a heroine to find him.