The ravens have their own 'Master Raven Keeper' - who is dressed in appropriately ridiculous garb and raiments and whose job it is to ensure that the ravens are looked after and their wings clipped to avoid them flying off and bringing Britain to ruin.
The ravens' presence at the tower is sometimes said to date back to medieval times, when crows still lingered in Britain's cities, and possibly attracted by the chance to feast on the bodies of the monarchs' enemies that hung from the gibbets and windows around the keep. Another version tells that the tale actually originates with the Celtic god Bendigeidfran - literally 'Blessed Raven'. It is said that he beheaded his enemy and buried his head under the tower, facing France as a warning to his enemies. Corrupted through the centuries, this tale became enmeshed with actual ravens.
Another often-told tale is that John Flamsteed - Charles II's astronomer royal - complained about the interference of the birds with his sightlines and equipment (read: 'shitting on his telescop'). Charles elected to dismiss the astronomer to Greenwich to keep the favoured birds near at hand instead.
In many ways, the choice of the raven is an odd emblem as crows have long been regarded as the harbinger of death or strife - no depiction of medieval England is complete without a carrion crow pecking at a body on the gibbet.
In fact, modern research suggests that the ravens' association with the tower may be nothing more than a Victorian embroidery.
A 2006 research project into the Tower's menagerie - which at one time included lions and giraffes - found no mention of ravens at all prior to 1883. In that year two illustrations were published (one a children's book) showing ravens at the tower. The first record of captive birds at the tower was as recent as 1918.
Nonetheless, so prevalent was the Tower's association with the birds by 1946 that the country was scoured for birds prior to its reopening after the war.