After being critically injured during a battle with a nanotech-enhanced foe, Stark injected his nervous system with an advanced nanotech-based weapon to save his own life. This fused Stark's armor to his body, allowing him to store the inner layers of the Iron Man armor in the hollows of his bones as well as control it through direct brain impulses. The Extremis enhancement has turned Stark into a cyborg, whereby the usage of his existing lockchip (a personal area networking implement implanted in his forearm) is directly integrated into his nervous system.