Origin
Briar was a normal human woman who happened to be in the wrong place at the wrong time. She witnessed a battle fought by Magneto. During this battle, she was accidentally hit by a piece of metal, which cost her the use of one of her legs. She later began to obsess about Magneto, wanting artifacts of him and wanting to understand him better.
Creation
Briar Raleigh was created by Cullen Bunn and Gabriel Hernandez Walta and first appeared in Magneto issue 5 (2014).
Major Story Arcs
Finding Magneto
Briar searched for Magneto for some time and eventually found him. Her goal was to help him in his war against bigotry and racism against mutants. At first, Magneto was reluctant to trust a human, especially one whom he had accidentally hurt. But eventually the two began to trust each other and eventually started a romantic relationship. This all changed when the incursions started to happen, which spelled doom for the entire world. Magneto left Briar in hope of stopping the Universal Incursion, but failed. This causes the events of Secret Wars, after which Briar was not seen again for some time.
With the Hellifre Club
More recently, Briar was seen again, seemingly now as a member of the Hellfire Club in New York City, among-side Magneto and others. What her role is, remains to be seen.