Simplify the following text for a Grade 5 native English-speaking person.
Original: The Mayor of London is mayor of Greater London , which has a population of over 7.5 million while the City of London is only a small part of the modern city center and has a population of less than 10,000 . The first elected Mayor of London is Ken Livingstone , who was re-elected in 2004 .
Simplified: The Mayor of London is the mayor of all Greater London ( including the City ) .