Short answers, pulled from the story.
Revolver Ocelot is based on veteran Western film actor Lee Van Cleef. Hideo Kojima designed the character to have Western tones and traditional gunslinger garb including a duster spurs and gunbelts.
The young version known as Major Adam Ocelot appears four decades before the original Metal Gear Solid events. He serves as a GRU Major under Colonel Volgin's command during that time period.
Revolver Ocelot uses self-hypnosis and nano-machines to act as Liquid's mental doppelgänger to trick the Patriots' AIs. He establishes a parent company for five PMCs fighting for the Patriots control over the world before appearing to die from exhaustion caused by a new FOXDIE strain injected by Drebin.
Troy Baker voices Revolver Ocelot in the English version while Satoshi Mikami provides the Japanese dub. This follows previous performances by Pat Zimmerman and Kōji Totani in earlier titles.
Revolver Ocelot was originally from the former Soviet Union and a former member of Spetsnaz who secretly wished for Liquid's and Big Boss's dream world. He took orders from the Philosophers and the KGB while also receiving orders from the Director of Central Intelligence.