Skynet (Terminator)

Skynet – the computer system created by the Cyberdyne Systems organisation in the Terminator universe – is responsible for the events of the Terminator movies in which machines attempt to kill John and Sarah Connor and take over the world.

Knowing that the Avengers would attempt to save the world in the event that Skynet try to take over, if indeed they existed in the same universe, Skynet would undoubtedly try to eliminate the heroes.

It would be awesome to see Hulk wading through hordes of T-800s, seeing Thor pummelling a T-1000 and being confused when it reformed from a liquid mess, seeing Skynet trying to hack into an Iron Man suit, or seeing Tony Stark and Bruce Banner trying to figure out time travel upon learning that machines had been sent back in time to destroy them.

The Avengers have now already gone up against a robotic foe and his similar-looking drones in Avengers: Age of Ultron, but the sheer variety of different models that would be on show in a battle against Skynet would make for awesome spectacle (the T-1000000, for example – awesome).