Bureau of Narcotics
The Bureau of Narcotics is a law enforcement agency in Grand Theft Auto IV, and is known as the Drug Enforcement Administration in the Grand Theft Auto III Era. Both are based off of the real life agency of the same name, and their main purpose is to combat drug smuggling and use.
GTA III Era
The DEA is mentioned several times in Grand Theft Auto: San Andreas and appears in Grand Theft Auto: Vice City Stories. They wear bulletproof vests with "DEA" written on the front and back in white capital lettering. They also wear a dark green or blue t-shirt and dark blue trousers. They are seen driving Landstalkers, Flatbeds and Cheetahs.
GTA IV Era
The Bureau of Narcotics features no prominent role in GTA IV, and is only mentioned in a news report on The Liberty Tree's website about a joint raid on a mobile meth lab (which takes the shape of a Boxville) with the LCPD and NOOSE. It is then revealed in another report that the Bureau seized the meth lab to educate people about the dangers of methamphetamine.
The only known agent is Albert Thomas, who acts as a spokesperson for the Bureau of Narcotics. His statements to The Liberty Tree imply that the Bureau is involved in illegal practices, such as helping cocaine smugglers in Vice City and producing and smoking methamphetamine.