In Masters history dating back to 1934, the oldest Masters winner is Jack Nicklaus.
Nicklaus became the oldest Masters champion in 1986, when he won the green jacket for the sixth time with a final-round 65 that helped him overcome a four-shot 54-hole deficit at the age of 46. Of course, that was the final time Nicklaus won the Masters, though he did finish a remarkable T-6 in 1998.
Mark O'Meara is the oldest first-time Masters champion, doing so in 1998 at the age of 41. He won in his 15th Masters appearance, setting the mark for the most times entered in the Masters before winning it.
The oldest major champion in golf history is Julius Boros, who won the 1968 PGA Championship at Pecan Valley in Texas at the age of 48 years, 4 months and 18 days.
Three-time Masters winner Phil Mickelson can become the oldest Masters winner and the oldest major winner in history if he picks up a fourth green jacket in the remainder of his career at Augusta National.