Jack Bauer is an American federal agent working for CTU.
Bart Simpson accidentally connects to his cell phone while contacting the school base for the mission (Bauer in particular intended to call Chloe O'Brian for schematics that were presumably related to his current mission while engaged in a shootout against armed men that presumably belonged to a terrorist cell that he had been investigating). Bart quickly turns it into a prank call. He realizes when Chloe O'Brian tells him it is actually a prank. Bauer later turns up at the school to find Bart and bursts into the school gym. He had abandoned all other missions to track Bart down, causing Shelbyville to explode behind him.