Jullius Tallow was a 3rd level Magician and Head of Internal Affairs. He was noted for his sharp nose and yellowish skin color.
His expensive tuned car was (flashbacks in book 2) damaged by the cricket ball of Jakob Hyrnek and Kitty Jones (Kitty was 13 years old). The ball landed on the windshield of the moving car which caused Tallow to crash the car.
Kitty filed a case against Tallow for assaulting the kids. Being charismatic and a magician, he won easily.
The Hyrnek family business was on reproducing books of magicians. As revenge for Jakob, they purposefully altered some words in the books ordered by Tallow.
Tallow (book 2 current events) became a political enemy of Nathaniel for a short time.
Later during Honorius's killing spree, all magicians were called to stop the afrit. The magicians went on to have joint summoning. All were finished summoning except Tallow, who was maybe trying to call a powerful afrit. He read something wrong from his book (The Hyrnek's scheme) and he was killed by the spirit (much to the amusement of Bartimaeus and the other djinn).