Simplify the following text for a Grade 11 native English-speaking person.
Original: Maurice Harold Macmillan , 1st Earl of Stockton , OM , PC ( 10 February 1894 â `` 29 December 1986 ) was Conservative Prime Minister of the United Kingdom from 10 January 1957 to 18 October 1963 .
Simplified: Maurice Harold Macmillan , 1st Earl of Stockton , OM , PC ( 10 February 1894 â `` 29 December 1986 ) , was Prime Minister of the United Kingdom from 1957 to 1963 .