One of the Royal Princes from way way back was engaged to marry a French Princess (When we weren't at war with 'em).
She was only sort of 14 like they were when they were engaged to be married in those days and was housed as decently close to her royal fiance at Westminster - at a friendls fortified house in Southwark.
She was referred to as L'enfant de castille (Child of the Castle) and we Brits being masters of foreign languages bastardised it to Elephant & Castle....
Also am I wrong or does old holborn tobacco have the elephant & castle on it too???
mel and david have it right-it was Queen Eleanor wife of Edward 1 who was the Infanta de Castille. When she died her distraught husband brought her body back to London burning crosses overnight at each stop. So she has also given her name to the sites of the "Eleanor crosses" which include Waltham Cross, Charing Cross and I think King's Cross.. Quite a lady.
The Elephant & Castle was actually a blacksmiths which was converted into a tavern in about 1760. The name is as thought came from either the Cutlers Company who dealt in ivory hence the link with elephants, or the Infanta of Castile. In the Middle Ages the elephant was often depicted with a castle on its back in heraldic scenes and you often see it like this in chess sets.