The next Marvel superhero to get his own movie is Ant-Man, a.k.a. Hank Pym, a genius and an Avenger with the ability to change the size of his body. The feat he's most known for however, is actually pretty unheroic: in the 1980s, Pym struck his wife—the single act that's defined Pym for many comic readers.
Pym hit his wife, The Wasp, during a story arc in which he was going to semi-betray the Avengers in an attempt to get back their trust (The Guardian's Ben Child has a recap of the complicated plot):
Originally, writers had not planned for Pym to be an abuser. Jim Shooter, who wrote the Avengers wife-hitting storyline, explained in a blog post that the backhand was supposed to be an accident:
In that story (issue 213, I think), there is a scene in which Hank is supposed to have accidentally struck Jan while throwing his hands up in despair and frustration—making a sort of "get away from me" gesture while not looking at her. Bob Hall, who had been taught by John Buscema to always go for the most extreme action, turned that into a right cross! There was no time to have it redrawn, which, to this day has caused the tragic story of Hank Pym to be known as the '"wife-beater” story.
Also fascinating is Shooter's psychological profile of Pym:
His history was largely a litany of failure, always changing guises and switching back and forth from research to hero-ing because he wasn’t succeeding at either. He was never the Avenger who saved the day at the end and usually the first knocked out or captured ... Meanwhile, his rich, beautiful wife succeeded in everything she tried. She was also always flitting around his shoulders, flirting, saying things to prop up his ego.
In other words, Pym is a failure, frustrated by his perfect wife. That by no means excuses Pym's actions, yet it does try explaining the roots of Pym's terrible act. We should also note that Pym and his writers have tried multiple times to say sorry for his actions.