Cassie is the daughter of Scott Lang, better known as the second Ant-Man. In fact, she served as his primary initial motivation to be a superhero, when her ailing health came with medical bills he couldn't quite afford.
After her father was killed during the Avengers' disbandment, Cassie was inspired to become a superhero in her own right, and —after having stolen Pym Particles for years— finally manifests the ability to grow and shrink in size at will, without the need of a suit. With this ability, she becomes one of the very first Young Avengers, christening herself as Stature.
She later joins the Mighty Avengers, as part of the The Initiative started because of the Superhuman Civil War, but unfortunately dies just as her father is brought back to life during the The Children's Crusade.
Cassie's death would remain permanent until 2014, when Doctor Doom (morally inverted from AXIS) resurrects her as reparation for having been responsible for her death in the first place. With a new lease on life, she reunites with her father and later returns to her life of superheroics, this time operating under the name Stinger.
Cassie has appeared in other media, most notably in the Marvel Cinematic Universe, portrayed there by Abby Ryder Fortson and later Emma Fuhrmann. Originally portrayed as a small child as played by Fortson, from Avengers: Endgame onward she's a teenager and time-shifted to Fuhrmann to match.
Cassie Lang appears in:Notable Comics
- Young Avengers vol. 1 (2005 — 2006)
- Civil War: Young Avengers / Runaways (2006 — 2007)
- Avengers: The Initiative (2006 — 2007)
- Mighty Avengers (2007 — 2010)
- Dark Reign: Young Avengers (2009)
- Avengers: The Children's Crusade (2010 — 2012)
- Astonishing Ant-Man (2015 — 2016)
- Marvel Cinematic Universe (2015 — present), portrayed by Abby Ryder Fortson in her first two appearances, and Emma Fuhrmann from her third appearance onward:
She provides examples of:
- Affirmative Action Legacy: In a way, to her father, who shared her powers.
- Action Girl: To be specific, she herself is the one who chooses to become a superheroine.
- Artistic Age: She was 14 years old when she first joined the team but was often drawn as much older looking.
- Back from the Dead: She's killed in Children's Crusade but is eventually brought back to life by Doom in AXIS.
- Berserk Button: Attacking her father, as Doom finds out (see below).
- Comic-Book Time: She was apparently aged up several years in the brief period between Geoff Johns' Avengers run and the debut of Young Avengers.
- Daddy's Girl: She adores her father and wants to follow his footstep.
- Did You Just Punch Out Cthulhu??: After she thinks he killed her father, she grows to the size of God Mode Doom and knocks him over.
- Broke Your Arm Punching Out Cthulhu: Doom promptly responds by killing her.
- Disappeared Dad: Her father, Scott Lang. As of Children's Crusade, not so disappeared.
- Domino Mask: She wore one — see the image.
- Fake Defector: She pretends to work for the Power Broker in order to trick him into giving her superpowers. She agrees to do one legitimate job for him though after she learns that the target is Darren Cross.
- First Father Wins: Cassie greatly adores her father Scott Lang and wants to follow in his footsteps in being a superhero. However, she has a strained relationship with her stepfather Blake Burdick, a police officer who cannot stand the world of superheroes the young girl loves, and he unsuccessfully tries to keep Cassie and Scott apart. In the events of "Avengers Disassembled", when Scott is killed due to the actions of an insane Scarlet Witch, Cassie retreats into herself, blaming Blake for being unable to understand her as her father always did. Though Blake does try unsuccessfully to be a caring stepfather, despite sometimes being distant toward her and seeing her as a "less than brilliant" girl, it is clear that Cassie favors her father over him.
- Heroic BSoD: She has one in Young Avengers Presents when she accidentally indirectly injures her stepfather. She shrinks herself to microscopic size and keeps shrinking the more she talks. Eli snaps her out of it.
- I Just Want to Be Special: After her resurrection, she becomes increasingly bitter and resentful over no longer having powers. She ends up forming an alliance with the Power Broker in exchange for a new costume and Pym Particles.
- In-Series Nickname: Cassie is short for Cassandra.
- Interspecies Romance: With Jonas, a synthezoid.
- Jumped at the Call: Was originally planning to join the Runaways but forced her way into the Young Avengers after she found out about them.
- Got the Call on Speed Dial: After being killed, when she was resurrected she found that she'd lost her powers. When the Power Broker launched Hench X (in Astonishing Antman), which offered the chance to get superpowers to use against the heroes, Cassie applied, intending to get her powers back and then bring the organisation down. She is given Pym Particles, a new uniform, a new codename: Stinger.
- Junior Counterpart: She has the powers of her father, Scott Lang.
- Psychoactive Powers: She grows when she gets angry and shrinks when she feels guilty.
- Sacrificial Lion: Killed near the end to hammer in that Children's Crusade is a tragedy.
- Sizeshifter: Her power is to make herself grow or shrink at will.
- Spin-Offspring: She became a superhero after Scott's death, and effectively took his place as far as the Lang family goes. This ended upon his revival, where she died, but quickly got better.
- Stuffed in the Fridge: Her death at the hands of Dr. Doom is what fuels Iron Lad's Start of Darkness, putting him on the path to becoming Kang.
- Superior Successor: While Scott needs a special suit to access his shrinking and growing abilities, Cassie's powers are completely innate.
- Younger than She Looks: She's the youngest of the team but it's hard to tell.