Azrael is the name of several fictional character in the DC Comics universe. They are a group of assassins who were created by The Order of St. Dumas to "enforce god's will". The name is from the traditional Angel of Death.
The character first appeared in the series Batman: Sword of Azrael, as Jean Paul Valley in 1992
He then became a supporting character in the monthly Batman titles, eventually taking over the role of Batman through the Knightfall/Knightquest/KnightsEnd story arcs.
The subsequent Azrael series, chronicling Valley's battles against the Order of St. Dumas, ran for 100 issues between 1995 and 2003. Starting with issue #47, it was retitled Azrael: Agent of the Bat in an attempt to boost sales by tying the series in with the rest of the Batman mythos, including Azrael as part of the team of Batman, Robin, and the new Batgirl (Cassandra Cain).
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Official Site: D.C Comics
Links: Wikipedia The Dark Knight Unoff. Guide to D.C Universe