Tisiphone
Tisiphone, along with Alecto, Goddess of Pain, and her sometimes lover, Megarea, Goddess of Jealousy, compose the Furies, who seek to bring violence upon the world for some unknown past grievance. Tisiphone is easily the most openly dark of the three, but she also has an overwhelming sense of justice... hers is not killing for the sake of killing, but killing to right a wrong. She is primarily worshiped by assassins and bounty hunters who agree with her violent sense of justice and, though they do often have a code that requires them to kill only those deserving... even if no one else agrees just what constitutes that.
The worship of Tisiphone is treated with suspicion at best in most lands, as her worshippers often work well outside the local legal system.