Greer Nelson, also known as the Inhuman Cross-Species Avenger Tigra, is a loyalist member of S.H.I.E.L.D.'s 3rd incarnation, founded by Phil Coulson within the ATCU. Once a former lab assistant, after exposure to an experimental super soldier serum, she was given the potential to achieve superhuman abilities.
Greer Grant was the recipient of two separate sets of superhuman abilities, one Scientific and one Inhuman. As a laboratory assistant to Dr. Joanne Tumolo, Nelson became involved in a physiological conditioning program that would enable a human being to attain his or her full physical and mental potential. in times of need and desperation, Dr. Tumolo had accepted private funding for the project from an anonymous source revealed later to be HYDRA. They planned to use Tumolo's conditioning equipment in their growing net of super soldier programs.
After learning that it was HYDRA that coerced her and had paid for the experiments, Tumolo had Nelson secretly undertake the experiment alongside HYDRA's volunteer Shirlee Bryant. She and Greer Nelson emerged from the battery of treatments with superhuman physical capabilities. With the process complete, Shirlee revealed her true attentions, attacked Tumolo, and sought to kill her. Greer used her new power to stop Shirlee, and hold her offf. Having suspected that HYDRA would kill her in the future, Tumolo rigged her lab to explode on command so that HYDRA could not get their hands on her research.
In Greer's fight they were almost evenly matched until Greer gained the upper hand and knocked her out. Greer tried to help her employer and friend out of the lab but Tumolo told Greer that the lab needed to be destroyed to stop it being in the hands of HYDRA, and that it could only be triggered manually. After Tumolo convinced her, Greer helped set up the final phases of destroying the evidence and left when Tumolo told her to. Tumolo then committed suicide by destroying the lab and all the samples as well as equipment. The only thing of Tumolo's work to survive was Greer Grant, who vowed to do everything in her power to bring down HYDRA, with her new abilities.
Using the knowledge from her time spent as Tumolo's assistant, Greer made a suit capable of supporting her abilities and in order to conceal her identity would use a mask, and calling herself the Cat. The Cat then plagued the criminal underworld looking for HYDRA sympathizers, and soon found herself looking for the Kingpin, a crime lord with ties to HYDRA. Unfortunately, he was in jail at the time of her vendetta, and so Cat found a remnant of Fisk's organization that relocated to Chicago and planned to attack with hopes of finding HYDRA intel. Unknown to Greer, HYDRA was aware of her activities, and deciding that she was the only way that they could recreate Tumolo's process, became concerned with capturing the Cat alive. One night during one of her beat downs on local crime, a HYDRA team led by the Brothers Grimm abducted Greer and took her to the Kraken.