There are a lot of questions that have been unanswered as to how Ant-Man is going to tie into the rest of the Marvel universe, but the latest rumor may shed some light on how the hero will find his way to the Avengers and how Iron Man will find an ally in a former side character.
Starlog uncovered a rumor last week that could show how Ant-Man will meet up with the rest of the Avengers in the form of saving one character, Black Widow, after she is imprisoned as part of the Superhuman Registration Act that will catalyst the Civil War plot.
According to the site, Ant-Man will take place alongside the events of Age of Ultron, the fall-out of which will spur on the Superhuman Registration Act. While Ant-Man is largely self-contained in nature, the references of the MCU will come from Pym's past as a scientist for S.H.I.E.L.D. in the '60s, having worked alongside Howard Stark, Arnim Zola and Alexander Pierce.
However, in this flashback sequence, Pym will supposedly also have a run-in with a young military hot-head by the name of Thaddeus "Thunderbolt" Ross, who was last seen in The Incredible Hulk and played by William Hurt.
They go on to add that S.H.I.E.L.D.'s downfall in Captain America 2 forced Pym into the private sector, which makes him vulnerable and essentially serves as catalyst for the events that follow in Ant-Man. They add that the rumors states that the shooting draft of Ant-Man's post-credit stinger shows the older Ross re-appearing to Pym, claiming he'd been sent by Tony Stark. When asked why, Ross allegedly responds, "Haven't you seen the news? We're at war."
The site also claims Ross will play a supporting role in Captain America 3, begrudgingly helping Tony Stark enforce the Superhero Registration Act and giving him military aid as Stark is hesitant to use his own technology post-Ultron.
They add that rumors of Black Widow's limited involvement in Captain America 3 is also true, as her character will be arrested for aiding fugitive superhumans in a power play by Stark (which will give actress Scarlett Johansson a break from the MCU to focus on her family), though the source says a potential Black Widow jailbreak in a future Marvel film may help bring Scott Lang's Ant-Man into the Avengers.