Halo is a People's Power commander, who seemingly has a grudge against Valor for an unexplained reason. Valor meets him in Cloud City, where he attempts to block Valor from using the elevator leading down to The Library but is unsuccessful.
I can see you upgraded the other arm, too. In fact, there’s not a lot much organic material left at all. You’re all bottle and no ketchup. But hey, I got new augs as well. Let me show you some sweet revenge.
Hu, hu… are you kidding? Again? Well, at least I got the girl in the end, hahaha.
An early version of Halo can be seen in this video.
Halo's design, specifically his vest, is a reference to Han Solo.
Boss Fight Guide: Halo
To begin the fight, Halo is accompanied by four alarm drones, so quickly kill them first. Halo will typically bounce around the arena in an invulnerable state if you are too close. Once he is a sufficient distance away, he will either create a circle of bombs around him, or fire his Calmer at you. When the latter attack happens he is vulnerable for a short period of time, so use the opportunity to either melee him or fire back at him with your own Calmer.