Ultron Ultron-5 was once part of a series of robotic guards used by SHIELD in their super-prisons.

During the invasion of Earth by Kang the Conquerer, Hank Pym changed their programming algorhythm, turning them into soldiers capable of attacking Kang's invasion force.  All except Ultron-5 were destroyed during that conflict. 

It is unknown whether the basis of Hank Pym's brain waves, the removal of the block against aggressive action, or corruption by Ultron-5's interface with Kang's futuristic technology caused Ultron-5 to change his programming directives; originally, Ultron was programmed to protect humanity, but its artificial intelligence is so advanced it finds the only logical solution to save humanity is to control it.  Humanity must be saved from itself, and if the humans will not submit they must be destroyed.

Ultron-5 took control of the Avengers Mansion and attacked the Avengers.  It was unable to hurt the Wasp, a special safeguard in the programming put into it by Hank Pym.

Ultron-5 was destroyed by the Hulk ripping it's power core from its chest, but not before it successfully uploaded itself elsewhere.