X years after the events of Metal Gear Solid 2: Sons of liberty, Snake has grown old. Accompanied by his old friend, Hal Emmerich (Otacon) he embarks on his final mission to defeat Liquid Ocelot once and for all. Ravaged with age, his genetic curse is slowing him down, He has to complete his final mission within six months...

Sometime between Metal Gear Solid 2: Sons of Liberty and Metal Gear Solid 4: Guns of the Patriots, Raiden is now the game's trademark Cyborg Ninja like Grey Fox and Ogla were before him. Theroy suggests that Raiden may have died or for some other reason requested to become the Ninja, but at this time details are unclear. His "pale" appearance is due to his white, synthetic blood. He can take down the Gekko Metal Gears with ease using his Sword. So far he has been seen fighting the Gekko's, fighting MGS2's Vamp and lying in a helicopter serverly injured perhaps after the fight with Vamp from the E3 2007 trailer.

Meryl Silverburgh hasn't been seen since Metal Gear Solid on the original Playstation until Metal Gear Solid 4. She is with an unit investagting PMC activity. She acts in part of a group of two other men using SOP for her team to "literally work as one" as she states. With this, they can share each other senses using their nanomachine network so all 3 peopel can act as one.

Drebin, as he explains in the Metal Gear Solid 3 TGS 2007 trailer, is a weapons wholesaler, a gun lauderer. He will take the ID tagged guns which you find on the PMC's and make some mods to them allowing you to use them yourself, as well as being able to add thing such as sites, grenade launch attachments etc. He appears to know more than Snake, and most, about The Patriots. His background is rather unclear. Noteably, on meeting Snake when he is asked who he is he replies with "Neither enemy, nor friend" a famous line used by Gray Fox in Metal Gear Solid.

EVA will be returning in Metal Gear Solid 4. She was last seen in Metal Gear Solid 3: Snake Eater after betraying Big Boss (Naked Snake). She returns in MGS4 as, of course, her older self. 50 years older to be exact, making her 78 years old. Where her aligences lie hasn't be revealed yet, however she does ask Snake to call her "Big Mama" which may suggest something. The Kojima Pro site however does list her as fighting against the Patriots.

Sunny is Olga's daughter which she asked Raiden to protect in Metal Gear Solid 2 before she died. Sunny reveals she is her mother in the trailer, as does Otacon when he mentions the Patriots took her away from her parents and she never met them. Aside from this, though, her appearance makes it rather obvious as she looks quite a lot like Olga herself.

Otacon is Snake's "Side-kick" so to speak. He is the original designer of Metal Gear REX. In MGS4 he serves once again as Snake's intel and support via Codec. It seems as though he will be looking after Sunny as well. He has invtented a built a romote control robot called MK. II which can be used by Snake and controlled using the Playstation 3's wireless SIXAXIS controller.

Vamp's name suggests that he is a Vampire as anyone would guess. This however has never been confirmed, but often hinted at by his immortality. Aside from being shot directly in the forehead, the shot has clearly made a scar on his forehead, drowned and shot again in Metal Gear Solid 2, he remains alive in Metal Gear Solid 4. In the E3 2007 trailer he is seen fighting Raiden and sustaining wounds which would be fatal to a normal human, however he is still very much alive. Kojima has earlier stated that Metal Gear Solid 4 will reveal how Vamp can survive through such wounds and how he is seemingly immortal.

As seen in Metal Gear Solid 2, Liquid Snake is taking over Revolver Ocelot through his arm. In Metal Gear Solid 4, Ocelot has almost if not completely been consumed by Liquid's arm and has now been named Liquid Ocelot.