The Story of Briar
Briar was created by the Black Rose — a secretive Noxian cabal that experiments with the boundaries of the possible. She began as a person. The experiments the Black Rose performed on her converted that person into something else: a being of pure, consuming bloodlust, whose hunger for violence is so total that the only way to make her remotely controllable was a restraining harness that suppresses most of her impulses most of the time.
The "most of the time" is the problem. When the blood starts, Briar's control collapses. The harness fails. Whatever vestige of her original self exists recedes entirely, replaced by something that kills with terrifying efficiency and absolutely no discrimination. She has killed the people she was pointed at and the people who pointed her. The Black Rose considers this an acceptable failure rate.
Somewhere in Briar, behind the hunger and the harness, there may be a person asking questions about what was done to her and why. She doesn't have the access or the vocabulary to pursue those questions yet. What she has is the hunger, the brief moments of coherence between feeding frenzies, and a slowly growing awareness that the people who made her did not do so out of kindness. That awareness is more dangerous than the bloodlust, in the long run.