A lot of people have been saying that they think you play as Big Boss in MGS3. I happen to think that you play as Ocelot, and I'll tell you why:
1. The game takes place in Russia in the 1960's (according to images from the trailer), the height of the Cold War. This could explain some storylines for Ocelot. Ocelot quote from MGS2:
Ocelot: "Mother Russia can ROT for all I care."
Gurlukovich: "When did you turn?"
Ocelot: "I abandoned her during the Cold War."
2. The character looks like Snake. Ocelot could be another project of Les Enfants Terribles, maybe the original clone, or maybe a son of Big Boss. Here's why: Ocelot has Liquid Snake's arm attached to him in MGS2. How else could Ocelot's body accept this arm, unless they had similar genetic information?
3. The Snake in MGS3 looks younger than Snake in MGS2. Since MGS3 takes place in the 60's, assuming the Snake in MGS3 is 20-30 years old, that would make Ocelot the age he is now.
4. MGS2's cliffhanger has to do with the patriots, and Ocelot is working for them, as far as we know.
5. Metal Gear Solid 3: Snake Eater. An ocelot (small tiger/large cat) in the wild eats snakes.
Plus, I think that MGS3 will do a Godfather Pt. II kind of storyline, switching from the 60's era to the present day (2010?) era of MGS.
Any thoughts/theories?