In the latest Halo book, set a few years before Halo 5, themonitor of Installation 00, Tragic Solitude, kills a team sent to Ark after the events of Halo 3. He spares one of the team and uses him to reactivate the Halo firing sequence. This is a plot to force the Ark's portal to Earth to be re-opened, as the monitor wishes to seek revenge against Humanity for damaging the Ark. He plans to sent thousands of Retrievers - Forerunner bots, to harvest Earth for resources, along with the rest of the Sol system, before re-firing the entire Halo array for shits and giggles.
Instead of just keeping the sole survivor alive, TS turns him into a shitty version of Robocop, with knives and blades in his hands. He needed a human to activate the firing sequence, as that's how the system works.
He also happens to be the brother of thesecond team member they send to Ark to stop the array firing. Funny how he always talks about his brother in case you forget that they are brothers. They are related. Brothers. Bros. Family. Brothers. He is brainwashed to kill on command! He defeats Tragic Solitude via his love and humanity. Ugh.
Wow, that's pretty bad. I'm glad I never bothered with any EU stuff post-Bungie because I'd probably be upset with the crap they're putting out. I'll just keep pretending it doesn't exist.