Mynx is an in-game character and a member of the Vindicators.
Katherine Stevens was a young college girl who voulenteered for a Crey research project. When the scientists discovered she had no living relatives and few friends, they used her to test a volitile serum which gave her feline features and abilities, including cat-like reflexes and razor-sharp claws. When she realized what they did to her, she broke free, scarring one of the scientists in the process.
She lived on the streets of Paragon City, sometimes committing minor crimes to survive, until she was rescued by Synapse and was given an opportunity to not only hone her skills but to also put them to better use.
Mynx was seen in several issues of the Top Cow incarnation of the "City of Heroes" comic series along with her sister Vindicators.
Mynx also appeared in Issue #2 of Golden Girl Comics.
Her Praetorian counterpart is Bobcat.
(Please see her Paragon Wiki entry for more information.)