William Brewster (c. 1566 – 10 April 1644) was an English official and Mayflower passenger in 1620. In Plymouth Colony he became a Separatist leader and preacher.illiam Brewster (c. 1566 – 10 April 1644) was an English official and Mayflower passenger in 1620. In Plymouth Colony he became a Separatist leader and preacher.