History
The Key is a demonic entity and the second half of The Lock. As a mystic infection, The Key bonds to a victim and finds out what they have the most emotional attachment to so that The Lock can track it down and destroy it. The purpose of this is to goad The Key's victim into murdering The Lock; as an infected becomes plagued with visions of dormant giant demons, killing The Lock enables them to fully manifest and wreck havoc. When Iron Man became infected by The Key, it sent out The Lock to murder extraterrestial immigrants that Stark had personally helped relocate to Earth.
Iron Man began investigating The Lock's murders after becoming aware of them on its fifth victim. He eventually killed The Lock in the Blue Area of the Moon before it could murder its final victims, opening the door to the invasion. Doctor Strange, who had been investigating Iron Man's visions at his request, arrived too late to warn him against killing The Lock, but he helped Stark stop the rampaging monsters. They headed to the D.O.M.E., where Strange used magic to extirpate The Key from Tony's body. The entity was then placed in a sample receptacle used by the D.O.M.E.'s systems to counteract its mystic energy and fire a destructive energy blast from its cannon that honed in on the invading monsters and destroyed them.[1]