Chances are, the majority of Marvel fans who are not comic-book readers might not have the slightest idea who or what Ant-Man is. The character is not the most popular Marvel has ever created, but he is very much important to the overall scheme of things.
The first Ant-Man is called Henry "Hank" Pym, and he is also the creator of the suit and the substance that allows for him to change size. In the upcoming movie, Marvel will be focusing on the second Ant-Man, Scott Lang. Compared to Pym, Scott is not a genius, but a thief who stole the Ant-Man suit to help his daughter who was suffering from a heart condition. With a little coaxing from Pym, the young thief later chose to become the new Ant-Man, and even managed to join the Avengers.
It is not certain if Scott Lang will be a thief in the movie, but from all indications, that could be the case. So far, we must add that the trailer didn't impress in any way, but since it is only a teaser, the real deal might get us more excited to see this film in July of this year.
Since the Ant-Man movie is set in the same universe as the Avengers, it is safe to say that he will eventually become a member of the team. We suspect several characters will leave, which would make way for the newcomers. Tony Stark might be the first to go, and maybe Black Widow after.
While we are not certain who will leave and who will take up the vacant spaces, we are sure that in the coming years, the new team won't be the same.
For the sake of history, we should probably point out that Ant-Man is a copy of DC's comic-book hero, The Atom. For those unaware, The Atom is a genius who created a suit that allows him to shrink to ant-like sizes, and even smaller in many instances.