Gabriel is an angel born in Heaven whose defining traits are his kindness and perception.
He worked at Aaru to help the pure souls enter Heaven.
Around the time Kya started his work forming the Angel Council - Azrael, the one in charge of Aaru, and a close friend of Kya, noticed Gabriel's abilities and thus recommended Kya to recruit him into the Council. Realizing he could do more good for Heaven, Gabriel agreed, and became the third member of the Angel Council.

He was the one to suggest the idea of idols to Kya as another way to earn more income. The idea was a success, since Heaven is now stable. Gabriel continues to help in other small projects, and is usually the one to run errands, sometimes with Jophiel, for the Council.
Gabriel still occassionally stops by Aaru to visit his old boss, and co-workers - bringing snacks, and to catch up with the progress of the new two-step program implemented by the Council.