Mr. Big/Story

Art of Fighting series
Mr. Big has been involved with the mob for as long as he can remember. A former kingpin of South Town, he was eventually overthrown by Geese Howard's organization. Nonetheless, Geese recruited Mr. Big, and he quickly rose through the ranks to become Geese's right-hand man.

While Geese was out of town on business, he left Mr. Big in charge. Under Geese's orders, Mr. Big has Takuma's daughter kidnapped as an added incentive to keep the unwilling father working for the organization. Unfortunately, the plan backfired when Ryo Sakazaki and Robert Garcia fought their way through South Town to rescue her and find Takuma, leaving Mr. Big defeated. Geese has soon returned to South Town, but luckily for Big, the former was far more concerned about dealing with the potential threat of his long-time rival Jeff Bogard, who had sought to expose Geese's criminal activities to the public, so Big wisely kept his mouth shut.

In the second game when Geese hosts the first "King of Fighters" tournament, Mr. Big enters as a contestant to prove his power to those who once defeated him while also hoping to defeat Geese and reclaim his status as South Town's undisputed kingpin.

The King of Fighters series
Mr. Big's life in this timeline is exactly the same as his Art of Fighting counterpart up until Art of Fighting 2.

The King of Fighters '96
In 1996, Geese recruited Mr. Big and Wolfgang Krauser to form a team and enter the tournament. Mr. Big accepted the invitation on the grounds of possibly expanding the influence of his organization. During the tournament's conclusion, it is revealed that Geese had used his fellow teammates to gauge the strength of the Orochi power. Enraged, Mr. Big tries to use a sniper on Geese, but is thwarted by Billy. He then leaves, warning Geese that he will one day return the favor again.

The King of Fighters XIV
In The King of Fighters XIV, in the South Town team ending, Mr. Big, referred to as James by Geese Howard, orchestrates an assault on their car, with Hein and Billy confronting the gunmen while allowing the crime boss to escape. The assault is likely the fulfillment of the threat he made back at KOF '96.

Neo Geo Battle Coliseum
This section is non-canon.

His story in Neo Geo Battle Coliseum serves as a prelude for his entry in the King of Fighters tournament. Mr. Big enters the coliseum and defeats WAREZ in a coup to drive them out of Southtown and increase the power of his own syndicate. As he celebrates his victory, he muses that he will enter the upcoming tournament to manage some way to take advantage of his future team members.