Simplify the following text for a Grade 15 native English-speaking person.
Original: John Maynard Keynes , 1st Baron Keynes , CB ( 5 June 1883 â `` 21 April 1946 ) was a British economist whose ideas , called Keynesian economics , had a big impact on modern economic and political theory as well as on many governments ' tax and economic policies .
Simplified: John Maynard Keynes , 1st Baron Keynes ( ; 5 June 1883 â `` 21 April 1946 ) , CB , was a British economist whose ideas have profoundly affected the theory and practice of modern macroeconomics , as well as the economic policies of governments .