The East End used to be the site of many of the London docks.
Historically it is one of the poorest areas of London. In 1888 the area became notorious as the site of the crimes of Jack the Ripper, and in the 1960s it was the area most associated with gangster activity, most notably that of the Krays.
Over the 20th century, the docks declined in use as they were replaced by deep-water docks elsewhere, and other forms of transport became more important. The East End is now home to various urban regeneration projects, most notably Docklands, a huge office and luxury housing development intended as an overspill area for the City of London.
It is the area where the BBC soap opera EastEnders is set, though to say it popularises the area is probably a mistake, as its characters live in eternal conflict with one another in rather dowdy surroundings.
Compare to West End of London.