I haven't read the Halo books, but his appearance in the game seems significant and Cortana and Chief act like they knew or know about him like's hes a significant being...but his entrance in the story for me was abrupt and made little sense.
Can someone explain?
GT: AncientToaster Speak of the devil...and he shall appear
It made little sense to everyone who doesn't know any of the lore outside the 3 game series, which includes me. But after like 10 minutes of reading and research, the concept isn't all that hard to grasp. Just go check out the wiki on him and the other Forerunners, you're gonna need to to understand this trilogy.