Rachel Leighton, also known as Diamondback, is a member of the Serpent Society.
After the death of her brother, murdered by Brock Rumlow, Rachel went to Taskmaster's academy as she thought she could only fend for herself with a criminal life. Her chalistenics teacher there was Blanche Sitznski, her future teammate Anaconda. When she found her street fighting teacher was Brock Rumlow, Rachel tried to run away, but Blanche found her, so Rachel instead cut her hair and donned a lot of make-up so Brock wouldn't recognize her.
After becoming Diamondback, Rachel joined the Serpent Society. When Viper took over the Serpent Society, Diamondback remained loyal to Sidewinder, carrying him to safety. She called the Society's old enemy Captain America for help, and while waiting had to face Fer-De-Lance and Coachwhip. After Steve Rogers (now in the identity of The Captain) and his allies came to Diamondback's help, they fought together against the Society. Anaconda trapped Diamondback with her constrictor arms, but Diamondback countered with an acid-tipped diamond. She was shocked to find that Cottonmouth had also sided with Viper, and saved Asp, Black Mamba and Bushmaster, who had been poisoned for remaining loyal to Sidewinder.
While Cap reached Viper's escape ship, Diamondback took Cap's allies in other ship for an air pursuit. When the water supply of Washington was contaminated with a mutagenic agent, Diamondback found Cobra and chastized him for betraying Sidewinder. She was later captured by the new Captain America, who believed her to be behind the citizens' mutations.
Diamondback and Cap's other captured friends were used by the Commission on Superhero Activities as a negotiation trinket to capture Rogers, but a recovered Sidewinder helped Diamondback to escape.
Years later, Crossbones caught Diamondback to regain the Red Skull's favor. Crossbones had Rachel under an abusive training until she became loyal to him, and then he made her steal samples of Steve Rogers' blood from the Avengers Mansion.
When Crossbones and Diamondback went to the Red Skull's mountain hideout in Colorado, they were "greeted" by Blackwing, Cutthroat and Jack O'Lantern. Crossbones threw a rope to Jack O'Lantern's ankle, and Diamondback jumped on his glider and threathened him with stabbing his heart with a poisonous diamond. This earned Crossbones and Diamondback an audience with the Skull. When Cutthroat heard Crossbones referring to Diamondback as "Rachel", he found out she was his sister.
The Red Skull allowed Crossbones back into the Skeleton Crew for a probationary period, and had Diamondback imprisoned. Cutthroat visited her in her cell and revealed his identity. He also told Rachel that he would kill Crossbones to ensure his place as the Red Skull's lieutenant.
Rachel knocked Mother Night out to escape, and then fought Blackwing for his glider, but was recaptured by Crossbones and found out that he had killed Cutthroat. She was used as a guinea pig to see if the stolen blood samples were genuine, but she escaped and helped Cap against Crossbones.