- "Trying to help people isn't dumb."
"Well, I screw it up just about every time."
"So, maybe you just need someone watching your back, like a partner."
- ―Cassie Lang and Scott Lang
Biological Father in Prison
Cassie Lang was born to Maggie and Scott Lang. Her father was a petty thief who vowed to quit his life of crime when his daughter was born; however, he was arrested after breaking into the house of the head of Vistacorp and sending back money the company had stolen from its customers. Cassie's parents divorced while Scott was still in prison and Maggie began dating Jim Paxton, who raised Cassie like his own daughter.
- "I'm not going to miss my little girl's birthday party."
- ―Scott Lang
A few years later, Jim Paxton hosted Cassie's birthday party. Scott Lang arrived, having been released from prison. The father and daughter hugged and Lang presented her with a gift of an ugly rabbit toy which she instantly loved. Despite Lang wishing to keep his brief visit a secret, an overexcited Cassie went to inform her mother of Scott's arrival; Maggie promptly spat out her drink in surprise. Maggie and Paxton spoke to Scott and, after talking in private, Scott left the party, waving goodbye to his disappointed daughter.
The night after the party, Cassie was being tucked into bed by her mother, who asked if she really liked the gift her father had given her; she assured her that she did because she liked its incredible ugliness. Cassie asked her mother if her father was a bad man because of the way she and Jim Paxton had spoken to him, but Maggie assured her that he was not, just complicated and easily confused.
Cassie joined her mother and Jim Paxton for dinner and they discussed Scott Lang, who had just broken out of prison with Paxton given the task of tracking him down. Cassie asked her stepfather if he was going to find her dad; Paxton told her he only wanted him to be safe. In response, Cassie told him that she hoped he did not find him.
Late Night Visit
The night before he undertook a new top-secret and highly dangerous heist under the leadership of his new employer Hank Pym, Cassie's dad, Scott Lang, put on the Ant-Man Suit and snuck into Maggie Lang's house, going into Cassie's bedroom and looking at her while she was sleeping. Happy with seeing his beloved daughter again, Scott continued to watch her for a while before enlarging himself and kissing her forehead. Once he was satisfied with his moment of seeing his beloved daughter, he left.
Saved by Ant-Man
Without warning one night, Maggie Lang's home was attacked by Yellowjacket while wearing a weaponized Yellowjacket Suit; Cross threw Maggie out the house and took Cassie hostage, telling the terrified child that he wanted to find and kill her father. Lang also questioned if Yellowjacket was a monster, something which the super villain did not deny.
Coming to her rescue, Scott Lang arrived moments later in the Ant-Man Suit and battled Cross, both shrinking down to minuscule sizes and fighting on Cassie's toy train set. Cassie watched in shock as tiny explosions occurred on her train set where the two fought and hundreds of Ants arrived and attacked Yellowjacket seemingly under Scott's command. Even more shocking was when Scott used some kind of device which caused her train set to instantly grow to gigantic sizes as well as one of the ants, which grew to the size of a large dog.
When Jim Paxton arrived, he tried to bring Cassie to safety, but Yellowjacket cornered them and attempted to kill them both. With only one chance left to save them, Scott Lang then shrunk down to the smallest size possible and attacked Cross, shrinking into his Yellowjacket Suit and damaging its internal mainframe, causing the suit to crush into itself and kill Cross and wipe him out of existence forever. For a moment, Scott was lost to the Quantum Realm, unable to stop shrinking, however he was able to repair his own suit and return to his original size. Once back in reality, Cassie hugged her father tightly. Shortly after, as the police rush up to her room, Cassie watched as her father made his exit as Ant-Man.
Months later, Cassie has adopted a giant ant as her new pet, treating it like a dog. Jim Paxton and Maggie Lang invited Scott Lang to their home for dinner to show their gratitude for everything he had done to protect their family. Paxton even informed Lang that he would not be going back to jail after breaking free the last time. Lang then received a call on his phone telling him to meet with Hank Pym and made a quick exit, kissing Cassie on the head as he left.
Cassie visited Scott during his two-year sentence of house arrest. They played together as Scott tried to keep her entertained without having to leave the house. He built a tunnel out of cardboard boxes for them to crawl through as they go in search of treasure. The treasure turned out to be Scott's "World's Greatest Grandma" trophy that Cassie gave to him. Cassie asked if she can take it for show-and-tell but Scott refused. They "escaped" down stairs that had been converted into a slide and ran into the fence. Scott accidentally put his foot through the perimeter, alerting the FBI that he'd left his house. They arrived to search the place just as Cassie's mom and Jim came to pick her up. Cassie left with her Mom but promised to come back. Unbeknownst to Scott, Cassie had secretly taken the "World's Greatest Grandma" trophy with her.
Wanting to be a Hero
Cassie called Scott looking for her soccer shoes, not knowing that he was currently being held captive by Ghost. As a result, she went to Scott's house to look for the shoes. The FBI arrived just after learning that Scott wasn't in his house. Cassie went upstairs and found an enlarged ant in the bathtub. She went back downstairs and tried to prevent the FBI from going upstairs by claiming that Scott was sick. Luckily, Scott made it home in time so as to not raise suspicion. After the Feds left, Scott and Cassie had a conversation about him being Ant-Man again. She told him that he needs a partner to watch his back. He thought she was talking about Hope, but then found that she was really referring to herself. Scott refused, explaining that if he let her help it would make him the worst parent. Cassie agreed that Hope was the better choice. Shortly after, she smiled as she witnessed her father, as Ant-Man, on television.
End of Scott's House Arrest
Scott immediately went to visit Cassie after having been let out of house arrest. She hugged him which led to Jim and Maggie hugging Scott too. Later, Hope, Cassie, and Scott sat in a shrunken car as they watched Them!.
Cassie survived the Decimation, but she believed her father dead. In reality, Scott also survived, but he was stranded in the Quantum Realm until his escape five years later. When Scott frantically knocked on the door to her home, Cassie could not believe he was alive at first, but she opened the door and cried in her father's arms, relieved to know he was safe and sound.
Reunited with her family
After the revival of all the Earth's heroes and the deaths of Thanos and his forces, Cassie was seen with her father and Hope watching fireworks, where both of them were happy to be reunited with each other.
- "I eat fear for breakfast."
- ―Cassie Lang to Scott Lang
Cassie Lang is usually happy and oblivious to most things and, like most children, she loves her parents without a second thought. She loves her father, Scott Lang, knowing he is a good man at heart; this bond between them is quite strong as despite three years apart, Cassie still loves and wants to be around her father. Cassie also appreciates her mother's boyfriend, Jim Paxton, despite she once stated that her father would be safer if the police did not find him. A few years later Cassie showed a knack for lying for others. She was able to buy time for her father when he needed a distraction.
Behind the Scenes