Vamp

However, Vamp survived.

Though the nanomachines within his body rendered him a sort of zombie, he retained his nearly immortal nature.

Under Liquid Ocelot, he took the reins of the BB Corps, and worked to support his uprising from the shadows.

Vamp's immortality was the result of nanomachines within his body that augmented his body's natural healing capabilities. As a result, he was unable to die, even should he wish to. The nanomachine technology in question stemmed directly from the research of Naomi Hunter.

When Snake suppressed the activity of those nanomachines, Vamp saw a chance to find death, and fought Raiden.

Vamp injected himself with the nanomachine suppressant, furnished by Naomi, and was at last granted the death he had so feverishly sought.