[@Arawak] The name itself should give away a large amount of it, it's a blatant rip-off of the HL2 Universal Union. They're meant to be a vastly superior force that's revealed to only be a scouting party.

EDIT: Also, they're the natural enemies of the Fallen. The UU knows the most about them and are trying to 1. prevent the heat death of the universe, 2. escape to another, newer universe or 3. succeed where the Fallen failed and ascend.