Final answer:
Steve Williams caddied for Adam Scott when he won the 2013 Masters, marking the first time an Australian won the tournament.
Step-by-step explanation:
The Australian golfer that Tiger Woods' ex-caddie Steve Williams helped win the 2013 Masters was Adam Scott. This victory marked the first time an Australian golfer won the Masters. With Williams on his bag, Scott won in a dramatic playoff against Angel Cabrera, making an impressive birdie on the second playoff hole at Augusta National Golf Club.