Early life[]

After Scott Lang was arrested for his illegal burglary activity with VistaCorp, his pregnant wife Maggie left him.^[3] However, despite her father's criminal activities, Cassie still adored Scott.^[1]

To prove his qualifications as a father, pay child support, secure an apartment, and get a job, Scott agreed to aid Dr. Hank Pym and Hope Van Dyne in stealing Yellowjacket's Suit and Pym Particles formula from the Pym Technologies.^[1]

When Scott and his team successfully destroyed the Pym Technology building and ruined Darren Cross's plans, a deranged Cross tried to exact revenge by threatening to kill Cassie. This lead to Scott and Cross battling in Cassie's room with her Thomas the Tank Engine set. Scott saved Cassie and stopped Cross by shrinking between the atoms of his suit, but went sub-atomic in the process. While in a state of delirium in the Quantum Realm, Cassie's voice calling out for her father brought Scott back to consciousness and allowed him to improvise a way back to regular size. Following the incident, Cassie kept an enlarged ant that Scott had increased in size during the fight as a pet.^[1]

Post-Civil War[]

Following the disagreement between Tony Stark and Steve Rogers which led to an all-out battle between the two heroes, Scott, who had been recruited to Rogers' team, cut a deal with the FBI allowing him two years on house arrest without contact with Pym or Hope. This free time allowed him to bond with Cassie more, especially by playing games and constructing mazes out of cardboard boxes to simulate shrunken adventures.^[4]

However, after Hope kidnapped Scott and brought him back into the fray as Ant-Man, Cassie managed to cover for her father with the FBI, including stalling them to allow Scott time to get back to the house. After this, Cassie asked him about his still being Ant-Man and suggested that he needed a partner, meaning herself, though Scott initially perceived her suggestion to mean Hope. After he was let off of house arrest, the two were able to spend more time together freely until Scott became trapped in the Quantum Realm again. ^[4]

Endgame[]

Cassie was one of the 50% of people who survived the Blip by Thanos' snap. In the five years following the Blip, she grew up under the assumption that her father had also fallen victim to the snap, not knowing that he had been trapped in the Quantum Realm. After Scott managed to escape (the five years having felt like five hours to him), he confusedly wandered around the city until he stumbled upon a memorial for those claimed by the Blip, and realized that Cassie was among the still-living. After this, he immediately returned to the house where she had grown up, only to find her alone and five years older. Eventually, after the Avengers resurrected the snap's victims, Hope included, Cassie joined her father and Hope in watching fireworks.^[5]

Quantumania[]

While after the battle with Thanos Scott decided to rest feeling his work was done, Cassie thought there were injustices to be fixed, being twice arrested while stopping acts of police brutality. In-between, she got closer to Hank Pym, who gave Cassie her own version of the Ant-Man suit, and helped her develop technology that would allow for communication with the Quantum Realm. Even if Janet Van Dyne wound up destroying the communicator, it still exposed the location of the Pyms and Langs to Kang the Conqueror, who proceeded to suck both families into the Quantum Realm.^[6]

• Pym Suit^[6]
• Pym Particles^[6]
• Pym Discs^[6]

• Cassie is portrayed as a child by Abby Ryder Fortson in the films Ant-Man and Ant-Man and the Wasp and as a teenager by Emma Fuhrmann in the film Avengers: Endgame and Kathryn Newton in the film Ant-Man and the Wasp: Quantumania.