Tosk was from the planet Alderaan, and he gained employment as a guard on the planet Cularin. During the time of Clone Wars, Lavina Wren, the senator of Cularin, was set to return to the world on a visit, and along with the guard Gibbs, Tosk prepared the security arrangements for her trip. Tosk killed a veshet, which he correctly deduced had been sent to attack Wren, and he ordered extra security precautions to be taken. Discouraged, Gibbs, who unknown to Tosk was an assassin hired to kill Wren, decided that Tosk was too competant to make a mistake, and so chose not to murder Wren during her visit.
Wren was later imprisoned on Coruscant by the Republic, and Tosk freed her and delivered to the Galactic Senate a recording in which Wren declared that the Cularin system was seceding from the Republic. The pair then escaped from Coruscant in a stolen starship, while coming under attack from clone troopers. The Office of Republic Justice subsequently placed a bounty of 20,000 credits on Tosk.