Uriel could not understand why Solomon would seal demons into pillars and summon them to spend time with when he was given, by God, the power to destroy them. He was given the responsibillity to either make Solomon ascend into Heaven or make him obey Heaven's laws. He hept punishing the man, often using torturous means; and when Solomon didn't cave - went after those closest to him and killed them. Kevin/Uriel later reveals that he was afraid of Solomon, and felt tremendous regret when he died, so much that he lost sight of himself for a thousand years. He also says that Solomon didn't blame him, even once.
William is Kevin's precious young master. Uriel switched with the real Kevin Cecil around the day of the funeral of William's parents, and stayed by William's side ever since. Uriel grew attached to William, protecting him, even feeling relieved when he could not give him Heaven's Exultation (ecstasy). His affection grew to the point where he would even choose William over Heaven, and go into Hell (with the existing possibility that the Round Tabe would make him Fall for such an action and Michael would take his other wing) to save/protect his young master. William didn't blame Uriel either for impersonating a close friend of his (actual Kevin), and deceiving him, to get closer to William.
Uriel is both very loyal to Michael and terrified of him. It was Michael who took one of Uriel's wings when the latter failed to bring Solomon to Heaven. Lately, however, Uriel has found something even more frightening (losing his young master William) than Michael's anger (but he would still not move against him).
Camio and Kevin have a mutual respect for each other. Even though they know each others identities, they have not confronted each other other than Camio revealing Kevin's identity as Uriel.
After revealing who he truly is to William, Uriel let more of his true nature (sadistic tendencies) show, with Dantalion usually paying the price (in bloody hands, which were targets for Uriel's feathers, aka darts... feather-darts?).