In the television series 24, the Counter-Terrorist Unit is an American governmental organisation similar to the FBI which specialises in detecting and removing terrorist threats. In the first series of 24, we follow the Los Angeles CTU head Jack Bauer as he tries to prevent the assassination of Presidential Candidate David Palmer. To add a twist to the tale, the assassins kidnap Bauer's wife and daughter.
In the second series, Bauer is pulled out of retirement to help discover a terrorist nuclear bomb and stop it exploding.
The makers of 24 had originally planned to make Bauer part of the FBI, but knowing that the storyline would involve double-agent plots that the real FBI would not like to associate itself with, they decided to make up a fictitious agency.