Greer Grant was married to William Nelson, a police officer in New York City. Unfortunately, her husband ran afoul of a rogue organization of cops calling themselves the Brethren of the Blue Fist. William Nelson was killed, but the Brethren were never uncovered.
Greer Nelson was the lab assistant of Dr. Joanne Tumolo, who was developing a process to enable a human being to attain his or her full physical and mental potential. Out of financial desperation, Dr. Tumolo had accepted private funding for the project from Malcom Donalbain, an eccentric former executive of the Brand Corporation, who planned to create an army of women warriors to serve him. Not trusting the test subject that Donalbain had coerced her to use, Tumolo had Nelson secretly undertake the experiment alongside the other woman. Donalbain's test subject, Shirlee Bryant, and Greer Nelson emerged from the battery of treatments with superhuman physical capabilities.
When Bryant died in a test of her abilities, Donalbain had his henchmen set off dynamite charges in the laboratory to make it appear that Bryant had died accidentally in an explosion. Tumolo was injured in the explosion. Believing her mentor to be dead, Nelson determined to stop Donalbain's plans. She donned one of Donalbain's specially designed cat costumes, and calling herself the Cat, thwarted Donalbain's plans and sent him to jail. Nelson soon learned that Tumolo had not been killed but had been hospitalized for apparent brain damage. During this time, Greer, donning the costumed identity of the Cat, became a hero in the Chicago area, battling villains such as the Owl, Man-Killer, Commander Kraken, and Man-Bull.
Unknown to Nelson, Tumolo was a member of the Cat People, a race of humanoids magically evolved from cats in Europe during the Middle Ages. Prior to the explosion Donalbain had engineered, Tumolo had become aware of a plot by the subversive organization Hydra to steal a bacterial culture that had been developed by Tumolo's ancestors. Hydra had discovered the secret of Tumolo's ancestry and suspected her of possessing the formula for "The Final Secret," or the Black Plague. Tumolo had chosen to feign brain damage in order to evade Hydra, but Hydra abducted her from the private home where she had apparently been convalescing. Nelson put on her Cat costume and pursued them. Hydra agents fled from the Cat's attack, but during the confrontation managed to shoot her with "alpha radiation," an unknown form of radioactivity. Dr. Tumolo revealed the truth about the Cat People, who performed rites upon Greer to save her life, resulting in her possession by a cat-soul. Greer was transformed into Tigra, a new incarnation of the Cat People's greatest champion. In this new identity, Greer defeated Hydra and continued her career as as an adventurer and also became a private investigator.
Although she was able to use the cat's-head amulet to change back to her human form, Nelson became so accustomed to and enamored of her feline form that she seldom made the transformation. Moving from Chicago, she became a full-time adventurer, encountering and defeating such menaces as the Rat Pack, Kraven the Hunter, Tabur, and the Super-Skrull. She also briefly worked with Red Wolf, Spider-Man, and the Fantastic Four. Tigra was among the handful of costumed crime-fighters that the telepath Moondragon coerced into vying for Avengers membership. She was elected to membership and served for several months, all that time doubting she was worthy of membership in the group. Although she proved herself while in battle with the Molecule Man, she decided to resign her active membership. Moving to San Francisco, she became friends with Jessica Drew, the original Spider-Woman.
Months later, when Hawkeye moved to Los Angeles to form a West Coast branch of the Avengers, she was invited to join. She made a staunch addition to the team, despite the fact that the human and feline sides of her personality had become at odds with one another, causing her behavior to become somewhat erratic. Because of her catlike need for attention, she became involved with teammates Hank Pym and Wonder Man at the same time. The ultimate solution to her discordant nature presented itself when she and the Avengers journeyed to the "Land Within," the magical dimension where the parent tribe of the Cat People dwelled. The ruler of the Cat People offered to magically cure her of her split personality if she would kill Master Pandemonium, a demonic human being whom the Cat People feared and hated. Although Tigra agreed, she could not bring herself to violate the Avengers' code against killing when she had the opportunity to do so.
After almost killing Hawkeye in a training exercise, Greer decided to abandon her Tigra form permanently. Almost immediately, demons Allatou kidnapped Hank Pym and Greer on behalf of the demon Allatou, who wrongly believed them to be agents of her enemy, Master Pandemonium. The Avengers sought aid from Hellstorm and Hellcat, who were retired heroes at the time, having set up an occult investigations business. Together, the heroes invade Allatou's realm with Pandemonium on their heels. A three-way fight breaks out until Allatou manages to strand everyone with Pandemonium aboard a boat running through the various realms of hell.
Shortly after, the castaways find that they have drifted into the Cat People's Land Within. It was revealed that the Cat People were demons, having become such through their longtime residence in the demonic realms. Tigra broke her promise to never again turn back into Tigra by using the amulet to change back into her Tigra form. The Cat People were at the time guarding a shard of Pandemonium's soul on behalf of Mephisto, and they had ordered Tigra to kill Pandemonium to protect it (which Tigra did not find out until then). The West Coast Avengers were shocked to find out that Tigra had agreed to murder Pandemonium in order to be rid of her second soul (Tigra), especially since it broke Avengers tradition. However, Hellstorm once being the Son of Satan very clearly understood what she was going through. Tigra was surprised to discover that Pandemonium was not really a demon, but was searching for the five pieces of his soul taken from him by Mephisto. Tigra refused to slay Pandemonium after agreeing to fight Pandemonium in the Cat People's arena after the Cat People had ripped his demon limbs off to make it as easy as possible for Tigra to live out her agreement, and the Cat People punished her by stripping away her cat-soul altogether and leaving her a helpless human. Hellcat, however, owning a version of Greer's original Cat costume, gave it to Greer, who led the Avengers in battle with the Cat-People and single-handedly defeated their champion, the Balkatar. The cat-soul was released from confinement when Greer knocked it over while trying to reach it with her grappling cat claws before the Cat King could release it back into her. When the container shattered, the cat-soul returned to Greer. Due to sitting and building up it's own strength, the cat-soul returned to Greer stronger than ever, producing a Tigra that is more physically formidable than ever and closer to what the Tigra legend her cat-soul was molded by. However, since Greer was wearing the Cat suit, which enhances her human abilities, she remained more controlled by her human side as she merged once again with the cat-soul. The Cat People surrendered, unwilling to battle a "whole" Tigra who now exactly resembled the revered Tigra of their legends. Returning with the Avengers, Tigra continued as an active member and forsook her previous romantic involvement with others of her team, but confronted Hank Pym of her change of feelings due to becoming a whole new Tigra while on vacation with Hellstorm and Hellcat.
The Avengers were rocked by controversy when their member Mockingbird revealed that she let the Phantom Rider die in a previous encounter. Sympathetic to Mockingbird's cause, Tigra joined Moon Knight in briefly splitting from the team to accompany Mockingbird, who quit the team and separated from her husband and leader, Hawkeye. Together, the threesome joined Bill Foster to stop the High Evolutionary, and later fought the Night Shift. Afterwards, the heroes sought help from Hellstorm and Hellcat to rid Mockingbird of the ghost of the Phantom Rider. The three parted ways after this, and Tigra returned adventure alongside the Avengers.
Over time, however, Tigra's cat-soul continued to reassert itself. As it gained more and more prominence, Tigra once again became moody and aggressive, but also began to change physically to resemble that of a predatory cat, and was even discovered to be chasing mice. On a subsequent adventure, Pym was forced to used his size-altering powers to shrink Tigra to the size of a house cat, which she resembled. He imprisoned her until he could discover a cure.
Shortly afterward, Immortus freed Tigra to further distract the Avengers from his plans against them, and Tigra roamed the city for some time. The sorceress Agatha Harkness, who at the time was living at the Avengers' compound, discovered and re-captured her. Seeking a cure for Tigra's condition, Harkness called upon the Cat People. The Cat People's new ruler-Tigra's old foe Tabur, a cat artificially evolved into humanoid feline form-appeared and restored Tigra to humanoid form. Tabur tried to coerce her into mating with him to legitimize his usurpation of the Cat People's throne, but Tigra resisted and Harkness mystically transplants Tigra's cat-soul into Tabur, causing him to revert to the form of a mere cat while allowing Tigra to keep her superhuman form but retain her human personality. Using Tabur's discarded amulet, Greer was even able to switch from Tigra form to ordinary human form and back again whenever she wished. Thus empowered again, Tigra rejoined the Avengers' West Coast branch.
Later, on a mission against their enemies, the Pacific Overlords, Tigra was forced to crash-land an Avengers Quinjet in an Australian wilderness, but was rescued by an indigenous tribe. She elected to stay with her rescuers, taking a leave of absence from the team. She did, however, assist a team of reserve Avengers when the main team was off-planet, fighting amid the Kree-Shi'ar War. Afterwards, she apparently remained in the United States and was on hand to attend the funeral of Mockingbird.
Tigra again joined the Avengers when they re-assembled all former members after a year-long hiatus during which many of their number were believed dead. Electing not to stay with the newly re-formed team, Tigra left with the Avenger Starfox for outer space, searching for hedonistic off-planet adventures. Ultimately, Tigra grew quickly disenfranchised with such a lifestyle and was relieved when former teammate Moondragon assembled Tigra, Starfox, and other Avengers to battle the alien Infinites. When the crisis was averted, Tigra returned to Earth.
When Tigra learned of a resurgence of activity by the Brethren of the Blue Fist, the organization responsible for the death of her husband, she helped the NYPD by going undercover to expose them. Tigra brought the Brethren to justice and stayed to complete her police officer training, beginning a new career.