She first appeared in Justice League Annual #2 (November 1984) and was created by Gerry Conway and Chuck Patton. She has been a member of the Birds of Prey and the Justice League.
Fictional character biography
Cindy Reynolds is born to suburban couple Edward and June Reynolds. When her powers of illusion begin to manifest at age fourteen, Cindy runs away from home, buying a one-way bus ticket to Detroit.
Once in Detroit, Cindy uses her chameleon and illusion-casting powers to protect herself. As she grows to adulthood, she adopts the identity of Gypsy, patterning her dress after the popular image of the gypsy. The Justice League would soon take up residence in a neighborhood near Gypsy's stomping grounds after Aquaman disbands the original League.
Shortly after the League moves into their new headquarters Gypsy begins to test and penetrate the League's security measures. Eventually, she becomes brave enough to follow along with them and to aid in the battle against the Overmaster and his Cadre. After this, Gypsy receives an offer to become a full-time member of the Justice League. Gypsy goes on to participate in the League's struggles against the power-mad Anton Allegro  and a reactivated Amazo.
Gypsy finds cause to test her powers to their limits when the new JLA is unexpectedly ambushed by the Royal Flush Gang during a wilderness retreat. While her teammates are incapacitated, Gypsy ventures outside her own body, in astral form. In this form, she can spy on the Gang's activities. Also during this mission, she receives a dire premonition about the fates of her teammates Steel and Vibe.
This League is doomed, though. In his bid to wipe out the new JLA, Professor Ivo sends an android to destroy Gypsy, but she manages to find its conscience and convinces it not to kill her. Though Ivo succeeds in killing Vibe (as she'd foreseen), the android sees Cindy safely returned to her parents' keeping.
Gypsy's domestic happiness is short-lived, as some time after she has left the JLA, a vengeful Despero arrives at her home and murders her parents. Gypsy would have been Despero's next victim, if not for the intervention of the Martian Manhunter and the rest of the Justice League. Devastated by the loss of her family, Gypsy is immediately recruited by Booster Gold to become a member of the corporate-sponsored team of heroes known as the Conglomerate.
Justice League Task Force
Over time, she grows very close to the Martian Manhunter, developing a sort of father/daughter relationship. The two of them are the mainstays of the short-lived Justice League Task Force. During her time in the JLTF, she is nearly forced to battle Lady Shiva in one early adventure, and is left for dead on another mission. She later joins the revamped Task Force along with L-Ron (in the body of Despero), The Ray, and Triumph.
Gypsy and Ray are both later mind-controlled and used by Triumph as during his strike against the reformed JLA; he expressed disgruntlement that their team had been ignored and forgotten when "the headliners" reformed. During the battle, she would see Aquaman, her old team-mate in Detroit, and say in confusion "you went away". 
There have also been hints of a romantic relationship between Gypsy and the Bronze Tiger. Gypsy and J'onn keep in touch. At one point, after she had been killed, Gypsy is resurrected by the Manhunter, who pleads with his Martian god, Hronmeer, to restore her life. She also aids Wonder Woman during a massive battle against Circe.
Gypsy joined Oracle's Birds of Prey. She has demonstrated greater flexibility with her powers as well, now able to extend her powers of invisibility to others and things around her. Gypsy also teams up with Vixen to clean up the remnants of an old case. The two heroines rescue Stargirl when after discovering that Amos Fortune was kidnapping members of the JSA.
Gypsy is one of the imprisoned heroes forced to fight on the behest of the Apokoliptan gods on Earth in the Dark Side Club. Gypsy is part of Martian Manhunter's funeral. She, along with several other heroes are telepathically compelled by the Martian Manhunter to recall Martian history. Later still, she is again accosted by Despero. The villain then brings her unconscious body to Happy Harbor and fights Vixen's ragtag Justice League.
Gypsy, Vixen and Doctor Light battle Black Lantern versions of several deceased Justice Leaguers that were attacking the Hall of Justice.
The New 52
Gyspy appears in The New 52 continuity, though no longer as a member of the League. She can be seen as one of the captive metahumans imprisoned by Amanda Waller in a government holding facility. She is a refugee from an alternate dimension, fleeing from Vibe's brother Rupture, a supervillain enslaved to Mordeth. Rupture reveals that Gypsy's full name in the new continuity is Cynthia Mordeth, as she is Mordeth's daughter.
Powers and abilities
Gypsy's primary power is that of illusion casting, which allows her to blend into her background, effectively becoming invisible. It also allows her to adapt to rapidly changing backgrounds without betraying the illusion. She can camouflage both herself and someone in close proximity to her. In Gypsy's first appearance, only her shadow is shown from the Bunker's monitor, and she appears to teleport at the end of the issue.
Gypsy's illusion-casting can also be used to project frightening illusions into the minds of other people. These illusions usually show what the affected person fears most. This ability can affect other living things besides people, and Gypsy can use this ability in combat situations. Gypsy has the ability to project an illusion to appear as another person, but that person needs to be her approximate height and weight for it to appear authentic.
Gypsy's powers have evolved to the point that she can now cloak not only herself, but a moving vehicle and its passengers. Gypsy also has limited precognitive abilities and appears to be able to project her spirit from her body.
Aside from her powers, Gypsy is an expert in hand-to-hand combat. She's also an accomplished acrobat, able to leap high, run fast, swim, and execute unexpectedly quick martial arts tactics with relative ease. Gypsy also has a strong aptitude in electronics and computers, and has become skilled in the use of firearms. She has been trained by Bronze Tiger.