Hank cracked under the stress of being a super hero/husband/scientist and turned into a royal jerk. He takes on multiple identities as he tries to resolve his feelings of inferiority, turning from Ant-Man to Giant Man to Goliath to Yellow Jacket. YJ is his most confident persona, but also his most cocky and arrogant. He abused Janet and was ineffective on the team. To prove himself, he created an AI Robot called Ultron, making it strong enough to best the rest of the Avengers. His plan was to swoop in and defeat it using a kill switch, regaining the trust of his wife and friends. Of course, it goes horribly wrong with Ultron disarming his own kill switch and escaping with the knowledge that his "dad" tried to kill him. Hank eventually loses his wife and retires for several years.
Ultron remakes himself over the years, first vowing to kill the Avengers, then all of humanity. It's a pretty cool story of a fallen hero that leads to some great down stream consequences. Ultron eventually repeats his father's mistake, creating a synthetic being called the Vision to attack the Avengers, and the Vision turns on him to join the heroes. The Vision was made using Wonder Man's brain patterns, which eventually creates a love triangle between the Vision, resurrected Wonder Man, and the Scarlet Witch. Vision marries the Scarlet Witch, and on and on. Ultron ultimately becomes one of the Avengers greatest heroes and a never-ending source of guilt for Hank. Who knows how they will approach it in the movie, but I just love that original story. Flawed heroes seem so much more believable to me.