(These are the origins of the sentinel from RvB: authors edition. I was the one who suggested it and UnknownNemesis98 was the one who put him in his first story be sure to check out the story,please :D)(Sentinel is Bungies not mine,just this one)

He was assembled on 2628.
He was named by a computer LOVE because he could never stay in one place for long.
His only assignment was to help anyone in need.
But on that same day his home was attacked by the covenant his people were enslaved by the brutes.
One day he escaped to look for help and eventually he floated to a canyon. He saw two bases a red and a blue one.
He decided to first check out the red base. He goes to it only to see that it's occupants are away. But finds pictures of the people living in it. The only thing he knows is that the people living in it are human. He gunfire outside to see a bunch people fighting goes up high to avoid being damaged. Sees the blue base goes inside and did the same thing he did at the red base except as he is about to leave hears a small meow. He spots a kitten beneath him and wonders what's wrong with it and sees that it is scared so to make it relax a bit he looks for something it could play with. He finds nothing so he just stays with it. A few moments later he hears on the other side of the wall someone yell "HUMAN SHIELD" followed by gunshots, struggle, and next thing he knew there was a hole in the wall and a person was on the floor wearing grey armor. The person looked a him confused and the only thing LOVE said was "who the heck are you?".
(This was a part of RvB:Authors Edition how LOVE got in the blue base. If any of you ask LOVE stands for Lots Of Vibrant Energy. RvB: Authors Edition is a story from UnknownNemisis98. Check it out if you can)