FBI

The Federal Bureau of Investigation (FBI) is a federal law enforcement agency charged with protecting and defending the United States.

Background
The FBI was established in 1908 as the Bureau of Investigation, the BOI or BI for short. Its name was changed to the Federal Bureau of Investigation (FBI) in 1935. The FBI operates under the jurisdiction of the US Department of Justice and the FBI is also a member of the U.S. Intelligence Community and reports to/ both the Attorney General and the Director of National Intelligence. The FBI investigates terrorism, serial murder, and several other serious federal crime.

Season 2
The FBI is first shown in Nightshifter when agent Victor Henriksen and other agents took over command of the police operation in an attempt to free the people supposedly taken hostage by the Winchester brothers in a bank and arrest the brothers. Henriksen was confident that he had Sam and Dean cornered when he sent SWAT agents in, but they escaped after they knocked out two SWAT officers and stole their uniforms to disguise themselves.

In Folsom Prison Blues, Henriksen succeeded in capturing the brothers, but it was a temporary victory, as the brothers had set themselves up to be captured. By the end of the episode, with the help of their lawyer and a prison guard, Sam and Dean escaped police custody again.

Season 3
In Jus In Bello, Agent Henriksen captured Sam and Dean again thanks to a tip made by Bela Talbot. While the Winchesters are held prisoner in the Monument, Colorado police station it gets attacked by demons. During the siege, Henriksen is possessed by a demon and it shot the unsuspecting sheriff. Once the demon was exorcised shortly after by Sam, Henriksen realized that the Winchester brothers weren't murderers after all and teamed up with them to defeat the demon attacking the police station. In the aftermath, he let them go, making it seem that they died in a fire to get the law off their backs once and for all. He and Dean also bonded, discovering that they are very similar with Henriksen admitting that he's frustrated with his job and only saving a few people and is envious of the Winchesters going around saving people everyday. After Sam and Dean left, Henriksen was tortured to death by a demon named Lilith and she also kills the other survivors.

Known FBI Agents

 * Adams
 * Morris
 * Calvin Reidy  (deceased)
 * Nick Munroe  (feigned, deceased)
 * Steven Groves  (deceased)
 * Victor Henriksen  (deceased)
 * Valente  (unknown)
 * Terrance Clegg  (deceased)