Even as he prepares for his 100th major appearance at the US PGA Championship, Phil Mickelson has his sights set on completing a career Grand Slam.
The American has had numerous near-misses at the U.S. Open - the only major he is yet to win - with six runner-up finishes.
While Mickelson would love to complete the set, something only five players have done in history, he said his Open win in 2013 was his biggest achievement.
"It's been my kind of career goal that I set out when I was a kid to try to win all four because it shows what a complete player you are to play under all those different conditions," he said at Quail Hollow on Tuesday ahead of this week's US PGA Championship.
"I think that's the real challenge because each major provides such a different set of challenges.
"But the greatest accomplishment for me, whether I win a U.S. Open or not, was winning the British Open. I thought that was going to be the toughest one for me, given the conditions and links golf, bouncing the ball up; and to be able to come out on top there was kind of a career-defining achievement, I feel."
This week Phil Mickelson and Ernie Els will play in their 100th major championship! Only 12 other golf legends have achieved this feat. pic.twitter.com/rulZgm62xl
-- PGA Championship (@PGAChampionship) August 8, 2017
Alongside Mickelson preparing for his 100th major is Ernie Els, the South African who has won four majors, as the duo join 12 others to have reached the milestone.
Els feels Mickelson, 47, is ready to win the elusive U.S. Open trophy.
"To win all four, one, you're going to need a special talent and a lot of determination," Els said.
"We are not all suited, as Phil says, to all the conditions we are faced with in the Masters, U.S. Open, The Open Championship and the PGA. They are all very different.
"You have to travel and then the last three are played, you know, very close together. To get the right form and all of that stuff is pretty tough.
"In Phil's case, obviously he needs the U.S. Open; finished second six times I think now. I think you know how to win it. That will be really great.
"There's only five guys on that list, and that's almost like the Holy Grail in our sport to win all four at least once."