Joker

Joker is a major character in Call of Duty: Advanced Warfare. He first appears in the level "Atlas". He is a member of Atlas Corporation, much like Gideon.

Biography
Joker joined the Atlas Corporation at an unknown time and circumstances, but became a excellent soldier. He seems to have been under the command of Gideon since his employment (giving him the nickname "Boss").

Rescuing P.O.T.U.S.
Joker appears alongside Mitchell to rescue the President of the United States, stealthily going through Camp David. Sneaking in, they fight their way through and rescue P.O.T.U.S. Once all troops seem to have been killed, Mitchell is tasked with extracting the president, they failed the test with Mitchell's new prosthetic arm malfunctioning, Gideon 'kills' P.O.T.U.S. and orders Joker to restart the course after Mitchell goes through training.

Rescuing the Nigerian Prime Minister
In Nigeria, he accompanies both Mitchell and Gideon to help Ajani rescue Nigerian Prime Minister Samuel Abidoyo from Hades and the KVA. The mission is successful, with Mitchell saving Abidoyo and the hostages in the van and the technologist. Afterward, Mitchell, Gideon, and Joker are enjoying a beer and crack jokes until Jonathan Irons comes in, telling them they did a good job and celebrates with them.

Nuclear Reactor Explosion in Seattle
He later fights to stop the reactor in Seattle, Washington from exploding due to the KVA taking over the reactor. Sadly they don't reach in time and must leave. Doing so, the reactors blows up the building and Carter dies, as he calls it. In the four years, Atlas helps the globe, providing food, shelter, and rebuilding cities and countries.

Danois in Detroit
Four years after the reactors destrcution, he accompanies Mitchell, Gideon, and Torres into what's left of Detroit to find Dr. Pierre Danois and capture him for information on Hades. once captured, they escape on their Hoverbikes as Atlas A.S.T.'s kill the rest of KVA troops.

Mitchell and Ilona leaving Atlas
After Mitchell and Ilona escape from Atlas in New Baghdad, Joker appears with Gideon, holding Mitchell and Ilona at gun point for their treachery (after getting evidence of Irons killing the Technologist). He is ordered to stand down, and watched Gideon let the two go with Cormack, the leader of the Sentinel Task Force. It is uncertain whether he stayed in Atlas or joined the Sentinel Task Force when Gideon defected.

Personality
Joker is a very skilled soldier and is a very good friend of Mitchell and Gideon, as shown in the post "Traffic" cutscene. It is unknown if Joker stayed in Atlas and fought in the war.