King Henry VIII bought the land from the canons of Westmister Abbey and turned it into a hunting ground. Charles I opened the site for the public in 1637. In 1733 the land was converted into a park. The "Hyde Park" is famous for the "Speakers' Corner" at Park Lane/Oxford Street.
St. James Park was named after a hospital that was already there, when King Henry VIII acquired the land. He built the "St. James's Palace" and used the land as a kind of zoo. In 1827 the park was redesigned according to the plans of John Nash.
Greenwich Park was once a royal hunting ground, which was opened in the 18th century for the public. You will have a very nice panorama from the famous "Greenwich Observatory" on the Thames and the skyline of the Docklands.
The "Regent's Park" is almost as large as the famous "Hyde Park" but it is rarely visited by tourists. In the park there is the "London Zoo" and a Boating Lake with pedal boats for rent. There are several cafes, a rose garden and an open air theater.