Who Cassie is and where she starts
Cassie is the reason Scott Lang becomes Ant-Man at all. In Ant-Man, Scott is fresh out of prison and desperate to be the dad his daughter already believes he is. She is maybe seven or eight, sweet and completely convinced her father is a good man, even when the rest of the family has doubts. That faith is the emotional engine of the whole first film.
She is not a sidekick yet. In the early movies Cassie is the person Scott fights to get home to, and the stakes stay personal because of her.
Cassie Lang's films in order
- Ant-Man (film, recommended)
- Ant-Man and the Wasp (film, recommended)
- Ant-Man and the Wasp: Quantumania (film, essential)
- Avengers: Doomsday (film, upcoming)
The first two are rated recommended because Cassie is a supporting player. Quantumania is essential: it is as much her movie as her father's. Doomsday is still ahead, and Marvel has not shared any details about her part in it.
How she grows up
Ant-Man and the Wasp finds Scott under house arrest after Civil War, and Cassie is the best thing about his days at home. She builds forts with him, cheers on his ridiculous escape attempts and tells him outright that she wants to be his partner one day. It is played for laughs, but it plants the seed.
Then the timeline jumps. After the five years Scott loses during the Blip, he comes back to a teenager. By Ant-Man and the Wasp: Quantumania, Cassie has her own suit, a habit of getting arrested at protests and a science project with Hank Pym that maps the Quantum Realm. That project is what pulls the whole family into the subatomic world, and the film tests whether she is ready to be more than Scott's kid.
The family around her
Ant-Man (Scott Lang) is the center of her life, and their relationship is the heart of every film she is in. The Wasp (Hope van Dyne) becomes a kind of mentor and bonus family member. Hank Pym is her science partner by the time she is a teen, a funny pairing of a grumpy genius and a kid who refuses to be talked down to. Falcon / Captain America (Sam Wilson) links her family to the wider Avengers story: Scott's very first run-in with an Avenger is a scuffle with Sam in Ant-Man.
Two actors, one Cassie
Abby Ryder Fortson plays young Cassie in Ant-Man and Ant-Man and the Wasp. She is a natural scene partner for Paul Rudd, and the improvised feel of their father-daughter moments is a big part of the charm. Outside the MCU she later led the coming-of-age film Are You There God? It's Me, Margaret.
Kathryn Newton takes over as teenage Cassie in Quantumania. She brings a sharper, more restless energy that fits a kid who grew up while her dad was missing. Newton is known for Big Little Lies, the body-swap horror comedy Freaky and Lisa Frankenstein.
What to watch, and in which order
Go in release order. Ant-Man is the best starting point, and Ant-Man and the Wasp is short, light and builds directly on the father-daughter story. Avengers: Endgame explains the jump in Cassie's age, so watch it before Quantumania if you have not already. After that, Avengers: Doomsday is the next title on her list.