Uriel is one of the archangels. Specifically, he controls light and is the eldest out of his brothers and sisters.
Uriel and Zadkiel were in a romantic relationship until Zadkiel stabbed Raphael and Michael then fled Heaven. Uriel loved her dearly and did not want to believe that Zadkiel was bad.
Uriel and Raphael were close friends up until Raphael made the decision to tell Satan about Titus before informing Heaven. Uriel no longer wants to be his friend and cannot trust him.