Like the other original Runaways, Molly Hayes was born after her parents and the other members of the Pride decided to pass on their inheritance from the Gibborim to their children. Molly's parents, Gene (a doctor) and Alice Hayes (a speech therapist), were telepathicmutants complete the Pride work. Molly was younger than the Pride's other children because it took them longer to conceive due to their mutant genetics. At birth Molly's parents tested her for the presence of an X-Gene, but the tests results were negative.
Along with Karolina Dean, Molly was not present to witness her parents and the Pride sacrifice Destiny Gonzales for the Ritual of Blood. She was also left out of the groups subsequent meeting at Griffith Observatory. The Runaways' last stop before going into hiding was rescuing Molly. After narrowly escaping their parents, and taking refuge in The Hostel, Gert suggested taking on new codenames to start over without the influence of their parents. Molly wanted to be named Princess Powerful, but Chase instead dubbed her Bruiser.
Molly thought that running away was a great adventure, and she was excited about becoming a real superhero and even made a costume. Molly has been a longtime admirer of superheros, and even planned on one day joining the X-Men and marrying Wolverine. Molly also owns a plush Doop doll and loves Dazzler's music.
Molly was the only Runaway to truly miss her parents, and had to be continually reminded that her parents were super-villains. Chase Stein and Molly began to develop a big-brother/little-sister relationship. Molly later developed a similar sibling relationship with Speed from the Young Avengers much to Chase's annoyance.
After narrowly escaping the destruction of the Marine Vivarium, the Runaways were immediately apprehended by Captain America and placed into foster care. Molly was picked up by a local branch of the X-Corporation. Weeks later after a text message from Karolina, the Runaways reconvened at the Griffith Observatory. Together they decided to retrieve Old Lace and the Leapfrog, and runaway again.
Molly was always excited to bring new recruits onto the team, but sometimes lacked some of the social nuances of young adults.
During a trip to New York City to help Cloak, Molly met her idol, Wolverine. However, she quickly became annoyed with him resulting her punching him hard enough to propel him out of a church window. This ended her crush on Wolverine.
Molly once encountered the Beast at the La Brea Tar Pits and the two discussed extinction. When Beast explained that mutantkind was heading in that direction Molly stormed off, calling him a depressing jerk. The two were able to reconcile when the Beast told her that, despite this, she should try to do as much as possible so she could be remembered.
After the X-Men relocated to San Francisco, Molly began complaining of the psychic call sent out to all mutants. Molly was able to tour Graymalkin Industries, but ultimately again declined the X-Men's offer in favor of remaining with her friends.
During a fight with Dragoness, Molly was knocked unconscious and awoke to find that she had been kidnapped by the Provost, who used children to commit thefts. Fortunately, Molly was able to organize her fellow captives, defeated the Provost, and returned home.
Molly took Gert's death hard. When she began receiving ominous direction from a disembodied voice, she believed it was Gert aiding her from beyond the grave. In fact, it was Alex Wilder trying to redeem himself and escape from Hell.
During their trip to 1907, Molly was extremely excited at the prospect of recruiting Klara Prast, a young girl roughly Molly's age with the girls of botanopathy and chlorokinesis. Upon returning to the present, Klara and Molly became best friends.
When Chase started to sense that Old Lace was still alive, the Runaways followed the trail straight to the Avengers Academycampus. When Justin Seyfert detected the Ultron tech within Victor and X-Genes in Molly and Klara, the Runaways were attacked. The fighting ceased and they made an effort to recover Old Lace. Much to the Runaway's joy they found Old Lace alive and well. They then came into conflict with the Academy again as their plans to force Klara and Molly to stay were revealed. Ultimately, Dr. Pym agreed to allow the girls to remain with the Runaways as long as they checked in regularly and took a robotic tutor for Molly and Klara.
When Nico and Chase disappeared with little notice, Molly became very concerned. She somehow knew they had been kidnapped, and was worried for Old Lace's health. Dr. Pym agreed to look into the matter, but unfortunately came up empty-handed.
Molly is a second-generation mutant, and has demonstrated the following abilities:
Superhuman Strength: The upper limits of her powers have never been tested. Molly is seen toppling monsters as large as skyscrapers (albeit while supercharged with magic), tunneling through miles of rock and lift a car with ease.
It has been speculated by some fans that Molly's super-strength is psionically based due to her parents' telepathy and the pink aura she emits when using her powers.
Their identical telepathic abilities and power signatures, their similar physical features, their comments about being "pureblood", and concerns about not being able to conceive has led to some fan speculation that the Hayes' union was incestuous.
Molly is known for various ridiculous animal hats.