Cockney is the term used to describe any person said to be born within the sound of the Bow Bells - the bells of St. Mary-Le-Bow Church ("Bow Church") - in Cheapside, London EC2.
St. Mary-Le-Bow, rebuilt from 1670-1682 after the Great Fire of London by Sir Christopher Wren, takes its name from the bow arches in the Norman crypt. Wren continued the bow architechtural pattern through the arches on the steeple, which is topped off with a large weather-vane (from 1674) in the form of a dragon. The church was destroyed in 1941, leaving only the steeple and two outer walls standing, but was restored in 1952-1962 with bells recast and rehung.
Cockney should not be used as a generic term describing any person born in or around the general vicinity of London.
Phespirit was born twenty miles to the east of central London but has often been accused of being Cockney by virtue of his Essex accent.
The Cockney gift to world culture is the phenomenon of Cockney Rhyming Slang - a code of speaking wherein a common word can be replaced by the whole or abbreviated form of a well-known phrase which rhymes with that word.
Cockney Rhyming Slang has been evolving in the East End of London since the sixteenth century. It is thought to have originated from the seamen and soldiers who used the London docks, from the Gypsies who arrived in the fifteen hundreds, from the Irish residents and the Jewish faction and from all the other ethnic minorities which have made up the population of the city.