Just read
Michael 001B was the first spartan that was attempted to be enhanced beyond the limits of a normal spartan. The experiments failed miserably and Michael went a little off the rails and began to become extremely violent. Michael was sent into solitary confinement in a training facility, but broke out, stole his armor, and began to kill anyone he saw in the facility. He is confronted by Laurie-348 ((before she was a spartan) and is shot by her own bullet being deflected at her in the neck. She is able to drain his shields enough for Michael's "creator" Professor Samuel Lunis to shoot him to death. Well not really because he is actually just in a coma and is sent to an even more secure facility. Years later, when the conflict with the Insurrectionists happens, the facility is destroyed, letting Michael escape years later and joining the Insurrection. Now that he's free, he goes to hunt down the one who got him locked up for years, Laurie, now known as the bloody blur. (They are siblings btw, but Laurie doesn't know that!) This is totally not a huge Halloween reference.