Diamondback (Rachel Leighton) is a character appearing in American comic books published by Marvel Comics. Originally depicted as a supervillain who was part of the Serpent Society, she was first introduced in Captain America #310 (October 1985) and became a series regular for years afterwards.

Rachel Leighton made her debut as part of the Serpent Society and soon came into conflict with Captain America as the group carried out an assassination. Later on Leighton started to develop feelings for Captain America, drawing her away from the Society to the side of the good guys. After Captain America helped foil a takeover by Viper, the two began to date. Because of her involvement with a super hero the Serpent Society voted to execute her, but her life was spared by her friends within the Serpent Society. Leighton, along with Black Mamba and Asp, formed BAD Girls, Inc. a trio of adventurers who would on occasion aid Captain America. During the "Civil War" storyline BAD Girls, Inc. sided with Captain America's Anti-Registration group. She later became an agent of S.H.I.E.L.D., before briefly returning to her criminal roots as part of Serpent Solutions.

Rachel Leighton first appeared in Captain America #310 (October 1985), and was created by writer Mark Gruenwald and artist Paul Neary.

Rachel Leighton was born in Austin, Texas. She was once a part-time sales clerk at a boutique, but later became a mercenary. In Captain America #319, she reveals to Captain America that she has a brother and that when she was younger was introduced by him to the super-criminal known as the Trapster. In exchange for weaponry that the Trapster provides her with, Leighton suggests that in return she prostitutes herself to the criminal. One of the members of the original Serpent Society, Diamondback was a seductively sly woman with expertise in hand-to-hand combat, being trained by Anaconda at Taskmaster's academy. Her gimmick was that she threw acid-laced or poison-tipped diamonds at her enemies. After her first confrontation with Captain America while on assignment to find MODOK, she was instantly smitten. Diamondback was assigned to take Captain America into custody from the Porcupine, but was reluctant to attack, concentrating her efforts on Porcupine instead. She later attempted to form a partnership with Captain America to locate the Scourge of the Underworld.

Viper staged a coup of the Serpent Society, causing several of her underlings to infiltrate as new members and setting Viper up to take over by force. Diamondback and their current leader Sidewinder escaped, recruiting Captain America's allies to rescue the Serpents who were still loyal to Sidewinder. After a fierce battle, in which Viper was defeated, Sidewinder abandoned the Serpent Society. Diamondback stayed on for a while under the new leader, Cobra.

Rachel was later revealed to have resigned from the Serpent Society, and somehow temporarily switched bodies with the X-Man Dazzler. This led, in part, to a confrontation between the Serpent Society and the X-Men. Diamondback later alerted Captain America to the Bloodstone Hunt. She aided Captain America in combat with Batroc, Machete, Zaran, and Baron Helmut Zemo. She also encountered Crossbones for the first time. Diamondback later accompanied Captain America to the Red Skull's Skullhouse.

Diamondback and Captain America eventually went on their first date, aided by Rachel's friends in the Serpent Society, Asp, Black Mamba, and Anaconda. She then battled the Black Widow, and acquired a new costume. Diamondback was eventually put on trial by the Serpent Society for her consorting with the enemy (most of the Society assuming, incorrectly, that Diamondback had betrayed their secrets to Captain America) and found guilty for her actions, and almost executed. She escaped with Captain America and Paladin's help, and later hired Paladin to help get revenge on the Serpent Society. Along with her best friends Black Mamba and Asp, she formed "BAD Girls, Inc." After a failed kidnapping attempt from Anaconda, Diamondback was taken aboard Superia's ship, and joined her Femizons under duress. While aboard Superia's ship, she was attacked by the Femizon Snapdragon, of whom Diamondback developed a phobia. After being rescued and then being used as a test subject by the Red Skull to see if the blood packets that Crossbones brought was really Captain America's blood, the super-soldier serum enhanced Diamondback tracked down and confronted Snapdragon, who died in the fight.

Later, there was a glitch discovered in the super-soldier serum that Cap was suffering from and Diamondback went to Superia in hopes for a cure. Using her as a test subject, there was a 50/50 chance that the cure would either work or kill Diamondback. As an added stipulation, if the test was successful, Diamondback had to serve Superia as the second Snapdragon. The experiment was a success, but she later got out of this deal when Superia was killed.