I imagine everyone has one or two...

Scythe - he is kidnapped from an orphanage at 13, forcibly addicted to drugs and then forced into prostitution. At 15, one of his customers beats him up. He refuses to make any more calls, so his pimp cuts off his drugs. Scythe kills the pimp and steals all the money in the house, as well as the hard disk from the computer where the pimp kept all his records. The police delay the investigation of the murder (so crooked cops can find and destroy any evidence the pimp left behind, although they say it is because they are waiting for a crime scene investigating team) and during the delay one of the crooked cops burns down the house.

Scythe uses his knowledge of the pimp's business to recover even more drug money. He buys weapons and starts hunting down and killing pimps and drug dealers, as well as crooked cops and other crooked public officials. In his spare time he kills muggers, gangsters and other crooks.

A newspaper reporter mentions that there is something devastating criminals like a scythe through wheat and the name sticks.

Don't know her name: A human female mutant. Her mutation is long life and youth - she looks as if she is 16 but she is really several thousand years old. She has made a study of magic throughout her life and is a very powerful magic user and has an extensive collection of magical artifacts from all over the world. She has never before gone public, but the advent of other heroes with super powers in the world convinces her to contact them. She doesn't tell anyone about her lifespan, but she occasionally makes references to past events as if she has lived through them

Just to make it explicit - I officially donate these characters to the public domain. Ta DAH!