Lodewicus Theodorus "Louis" Oosthuizen (/ˈluːi ˈwʊsthaɪzən/; Afrikaans: ; born 19 October 1982) is a South African professional golfer who won the 2010 Open Championship. He also holds the distinction of finishing runner-up in all four major championships: the 2012 Masters Tournament losing in a sudden death playoff, the 2015 U.S. Open, the 2015 Open Championship where he was defeated in a four-hole aggregate playoff, and the 2017 PGA Championship. He is the seventh golfer to accomplish this feat, joining Craig Wood, Jack Nicklaus, Arnold Palmer, Tom Watson, Greg Norman, and Phil Mickelson. His highest placing on the Official World Golf Ranking is fourth which he achieved in January 2013.
Oosthuizen was born in Mossel Bay, South Africa. His early career was supported financially for three years by the foundation of fellow South African golfer Ernie Els. He won numerous amateur titles before turning professional in 2002 at the age of 19.