Nesbin was the leader of a group of Outsiders which included Presta, Ablif, and Jasko.
Like all Time Lords, Nesbin was taken from his family at the age of eight for the selection process in the Drylands. Staring into the Untempered Schism as part of a Time Lord initiation rite, Nesbin reacted by running away from what he saw in the Schism. (PROSE: A Brief History of Time Lords)
It was Nesbin's group who discovered Leela and Rodan after they had left the Capitol. Together, they organised an attack on the Capitol to fight off the invading Sontarans. (TV: The Invasion of Time)