Joker joined the Atlas Corporation at an unknown time and circumstances, but became an excellent soldier. He seems to have been under the command of Gideon since his employment (giving him the nickname "Boss").
Joker appears alongside Mitchell to rescue the President of the United States, stealthily going through Camp David. Sneaking in, they fight their way through to rescue P.O.T.U.S. Once all troops seem to have been killed, Mitchell is tasked with extracting the president. However, his new prosthetic arm malfunctions, resulting in Gideon 'killing' P.O.T.U.S., causing Mitchell and Joker's failure of the test. Gideon then orders Joker to restart the course after Mitchell goes through training.
Rescuing the Nigerian Prime MinisterEdit
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 celebrate the mission, until Jonathan Irons comes in, exclaiming his pride in them and sharing in a drink.
Nuclear Reactor Explosion in SeattleEdit
He later fights to stop the reactor in Seattle, Washington from exploding due to the KVA assault. Sadly, they don't reach it in time, and the reactors explode, killing Carter, a squad member, while the others are able to escape. In the next four years, Atlas helps the globe, providing food, shelter, and rebuilding cities and countries.
Danois in DetroitEdit
Four years after the reactor's destruction, Joker accompanies Mitchell, Gideon, and Torres into what's left of Detroit to find Dr. Pierre Danois and capture him for information on Hades. Once Danois is found, they escape on their Hoverbikes as XS1 Goliaths kill the rest of KVA troops.
Mitchell and Ilona leaving AtlasEdit
After Mitchell and Ilona escape from Atlas in New Baghdad due to Irons betrayal, Joker appears with Gideon, holding Mitchell and Ilona at gun point for their supposed treachery. 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.
Joker is a very skilled soldier and a very good friend of Mitchell and Gideon, as shown in the post "Traffic" cutscene. He can be very competitive, as seen in the "Traffic" cutscene and is very relaxed in nature. Despite this, he is also determined when he wants to be as evident in the start of "Atlas", and can also be unnerved when the situation presents itself as seen in "Fission". He is also realistic and is quick to realize when the situation is going to turn bad, as he was the only character to realize that the Vekron Pacific Reactor could not be saved, and tried to get Gideon to retreat.