There are several great professional golfers who swing left handed. Phil Mickelson is probably the most well known and the highest regarded left-hander. Bubba Watson and Mike Weir are also accomplished left handed golfers.
The most famous professional golfer that swings left handed is Phil Mickelson. He is actually right handed but learned to play left handed from standing watching his father play when Phil was very young. Phil Mickelson is considered one of the best golfers in the world and has an excellent short game.