Corporation Of London
The ruling body of London's financial district, the City of London. As such it is the equivalent of a standard London borough council, but it is ancient ("older than parliament itself") and has an idiosyncratic democratic structure with votes allocated to Square Mile employers rather than residents.
As its website explains, the Corporation's responsibilities extend far beyond the City boundaries in that it also provides a host of additional facilities for the benefit of the nation. These range from open spaces such as Epping Forest and Hampstead Heath to the famous Barbican Arts Centre.
The Wikipedia article contains more detail.