Quoting from wikipedia
In the E3 2006 trailer for Metal Gear Solid 4: Guns of the Patriots, Raiden appears fighting GEKKO units and wearing a Tokugawa Heavy Industries exoskeleton which strongly resembles those utilized by cyborg ninjas Gray Fox and Olga Gurlukovich. According to lead character designer Yoji Shinkawa, Raiden is "falling apart" and has had most of his body parts replaced by cybernetic prosthetics; the only parts of his original human body which remain are his head and spine. He also appears extremely pale - due, according to Hideo Kojima, to the fact that his blood is white (this could be Oxycyte, a blood substitute that carries 50% more O2 to the body). Despite the dramatic physical changes he has undergone, he appears to have retained his memories of his previous experiences with Snake and FOXHOUND, and tells Solid Snake in the trailer, "It's my turn to protect you."
Although Raiden will not be a playable character in MGS4, he will be constantly present throughout the game serving as Snake's backup. He will reportedly be playable in the next iteration of Metal Gear Online, which will be included as a special feature on the MGS4 disc.
In publicity material released for MGS4, Raiden is depicted holding an infant. Many assume that it is Olga's, which at the end of MGS2 was a hostage of the Patriots. However, as his lover, Rosemary, was pregnant as MGS2 came to a close it could be his own. The actual identity of the child therefore remains unknown.
