Vansell (full name Vansellostophossius) was Coordinator of the Celestial Intervention Agency. He was a determined person who did his utmost to keep Gallifrey in its position of power, and to maintain the Web of Time.
Biography
The Doctor knew him at the Prydon Academy. The Doctor (supposedly) called Vansell by the nickname of 'Nosebung'. (BFA: Neverland) Vansell belonged to the Deca, a clique of young Time Lords and Ladies which included the Doctor and the Master. Like Ushas and Rallon, Vansell did well for himself and had already received his Rassilon Imprimatur before the Doctor and the others. Vansell had already joined the CIA despite his youth and followed their orders to watch the Doctor closely (PDA: Divided Loyalties).
Angered at the fact that he believed that the Doctor had let the Nestene Consciousness escape destruction by the Time Lords, he set up a trial for him on Space Station Zenobia (PDA: Synthespians™) The jury would subsequently acquit the Doctor of the charges (DW: The Ultimate Foe)
Vansell led an expedition into the world of Anti-Time to find what he believed to be the body of the Time Lord's revered founder, Rassilon. He became possessed by anti-time energy, and attempted a coup. After overcoming the possession by the anti-time energy, he was killed when he assisting Lady President Romana. He was trapped within the Time Station's temporal reactors and was vaporised. (BFA: Neverland)
Alternative versions
In an altered timeline he attempted to kill the Doctor on multiple occasions. (BFA: The Sirens of Time)