Just announced at Comic-Con, Corey Stoll will be the bad guy in the new Ant-Man movie. He will be playing Darren Cross. Now Cross is not a new character, he is actually vital to the origin of the Scott Lang version of Ant-Man and since that is who Paul Rudd is playing, it makes sense to have Cross as the villain. But having him also be Yellowjacket, another of Hank Pym's (Michael Douglas) personas is an interesting twist.
Here is basically a synopsis the origin of Scott Lang and Cross' involvement from Marvel Premiere #47-48 in 1979.
Darren Cross is a villain of the Scott Lang version of Ant-Man origin. Head of Cross Technological Enterprises, he grew the company to rival Stark and Hammer. But Cross was diagnosed with a rare heart condition and used his tech to create a nucleoganic pacemaker to save his life. The device worked but it mutated Cross giving him superhuman abilities but also he was burning out his heart quickly. Heart transplant would work but only last for short periods of time.
This led him to kidnap Doctor Erica Sondheim to save him and unwilling donors from the slums. Scott Lang was also in need of Sondheim to save his daughter Cassie, leading the ex-con to steal the Ant-Man costume to try and rescue the good doctor. A battle between Cross and Ant-Man lead to Cross burning out his heart and dying.