History
Cassie is Scott Lang's daughter. At some point she got sick from a rare disease, leading Scott to use his engineering abilities for theft. He was caught and, while was released from prison around the time Cassie got well, his career was ruined. As a result, he took employment as maintenance man for Graybrun College, which was also the place of employment of Hank Pym, the Ant-Man. Scott's former criminal partner, William Cross thought that Scott still had some money from the theft and wanted it back, kidnapping Cassie and threatening to kill her if he didn't receive his money.
Scott stole Pym's Ant-Man suit and Pym Particles in order to easily steal money and save Cassie. When he arrived at his meeting with Cross, Cross realized the advantages he could take gain from Scott's powers as Ant-Man, and determined to force Scott to keep working for him. In that moment, Pym, and the Heroes for Hire arrived to save both Scott and Cassie. Using "Pym disks", Hank shrunk Cassie to keep her safe while Lang went to her rescue. Iron Fist and Luke Cage started fighting Cross' thugs. They easily took down Comanche, Cockroach Hamilton, Gideon Mace, Piranha Jones, Big Ben, and Señor Muerte.
Lang took Cassie to safety as Pym protected himself from Cross' shots. Scott punched Cross through the room and told him not to ever mess with his family again. When the villain asked what is he gonna do, he ordered ants to attack him and finally knocked Cross out with a single punch.
After realizing the good job Scott had done, Hank officially passed the mantle of Ant-Man to Scott.[1]