Zadkiel ("righteousness of God") is an angel of the choir of Dominations. As such, he is the prince of this choir and the second lowest in rank of the seven angels of divine grace. Zadkiels prominence is all but ignored by the other children of fire. He is referred to (though not in his presence) as the forgotten one.
But Zadkiel is far from being worthless. His duties and obligations are numerous indeed. Among these duties, Zadkiel serves as the angel of benevolence, mercy, and memory. He does, however, seem to work more through other angels than the others of divine grace do. Rarely is he seen outside the Seven Heavens.
Only one notable exception to this has occurred. It was Zadkiel who stayed the hand of Abraham when the patriarch sought to sacrifice his son, Isaac, to the Almighty. Save for this incident, though, his presence on Earth is a rarity. His underlings, however, have a very strong presence among the children of clay.
Along with his other duties, Zadkiel, with the help of Zophiel, has been known to assist Michael when he goes into battle. Such epic confrontations have become rare in modern days, and so this duty has become less demanding for him.