The raven is a larger cousin of the crow. A group of them is called an unkindness. European Christians, with their dim view of the dark-complected, saw them as harbingers of death and woe. Earlier people considered them gods specializing in knowledge and mischief.
In real life, ravens are intelligent, social birds. They are omnivores, attracted to human settlement by trash and road kill. They are known to play with toys, to defend their territory, to trick one another, to torment lesser animals. Adolescent ravens roam in gangs; adults mate for life. Famous ravens include Edgar Allen Poe’s late-night visitor, the dream lord Morpheus’ friend Matthew, and Terry Pratchett’s Quoth.
There is a superstition that Great Britain will fall if there are ever fewer than six ravens at the Tower of London. Today the Tower ravens are domesticated: their wings are clipped, they have names, they are fed a carefully managed diet including vitamin supplements, and some live longer than 40 years. Their care and function has been compared to that of British royalty. They may or may not be battery operated.
More ravens, and other things, here. (SPOILERS at the link!)