In his own mind, the "Golden Bear" finished with truly competitive golf in 1996, signing off with two wins on the Seniors Tour, taking his career tally to 116 worldwide.
Although he continued to make appearances at the majors -- tying for sixth at the 1998 Masters -- and in the occasional PGA Tour event, it was the world of business and his charity work with his wife of 55 years, Barbara, that dominated his day.
The work ethic was always ingrained in a man from a family of German descent, and even now -- having turned 76 on Thursday -- he has a punishing schedule.
"I will probably die with my boots on, but that's okay!" Nicklaus told CNN.
"It's not about money for me, I think I passed most of my part of the company off to the kids years ago.
"I don't mind dying penniless right now -- but just not right now," he adds with the laconic humor for which he is renowned.
His two great rivals in the "Big Three" -- Gary Player and Arnold Palmer, who helped him transform golf in the early 1960s from a country club pursuit to a major global business with massive sponsorship and prize money -- are also made of the same stuff.
Like Nicklaus, they all have varied business interests.
"We played golf and continued to play for most of our life, and the people you get involved with in business are people who like golf and followed us through the years and they really enjoy the association," he says.
With a few metaphorical visits to sand traps and the rough on the way -- the 2008 global financial downturn hit the golf industry hard -- Nicklaus is proud of his business success; his companies sell anything from ice creams, fine wine and lemonade to the obvious areas like golf balls and equipment and course design.
Linking up with billionaire banker and investor Howard Milstein, who bought a 49% stake in the Nicklaus Companies group for $145 million in 2007, has helped him diversify his interests with a strong emphasis on branding, identifying his name to a whole range of products.
"I figured branding has to be the future, something to last not only in my lifetime but to create a legacy beyond my lifetime," Nicklaus says.
A percentage of the proceeds from some sales goes to children's healthcare -- a tradition that started with an emergency involving Nicklaus' first daughter Nancy.
"She was less than a year old and we found her choking. We took her to the Columbus (Ohio) children's hospital and they found a crayon lodged on the windpipe," he recalls.
"It was touch and go for a while but the hospital saved her life, and Barbara and I said that if there was anything we could ever do for children, we would do it."
Philosophy of philanthropy
As well as serving such worthy causes through business, Nicklaus also donates millions of dollars to a children's hospital and other charities through the leading PGA Tour tournament he hosts -- The Memorial.
In recognition of his sportsmanship, leadership and philanthropy, Nicklaus received Sports Illustrated's Muhammad Ali Legacy award on December 15, capping an incredible 2015 in which he also received the Congressional Gold Medal, only the seventh sportsman to do so, in an emotional ceremony in Washington.
Milstein, whose family company and foundations have donated over $3 million to survivors and first responders in Hurricane Katrina and Hurricane Sandy, said the ethos of giving had helped him and Nicklaus to build trust in their business dealings.
"We believe in stepping up when you can and doing the right things," Milstein told CNN.
The 63-year-old believes it was one of the reasons Nicklaus chose him to be his partner in a "beauty parade" which also included private equity firms, who might have been tempted to sell on their share to maximize profit.
Milstein insists he's in it for the long term, but the timing of his acquisition could hardly have been worse, with the full impact of the global financial downturn leading to tough trading conditions.
Nicklaus had originally committed to providing his services for five years to promote the brands before stepping back, but is working as hard as ever.
"I felt Howard didn't get a fair shake to realize the value of our company," he explains.
Milstein was not going to persuade him otherwise, and would probably not have succeeded if he had tried. "He's a perfectionist with the attitude of a young man always looking to do better," the younger partner says.
"I've told my company I will work as long as I can be effective," adds Nicklaus.
But it's not all work and no play for a very active septuagenarian. Most of Nicklaus' leisure is time spent playing tennis -- he has well-tended grass courts at his Florida home -- and watching his children and grandchildren in their various sporting endeavors.
One grandchild, Nick O'Leary, was a Florida State football star and is on the Buffalo Bills' roster.
"Barbara and I go to about five or six games a week," Nicklaus says.
He met his wife in their first week at Ohio State, where Nicklaus chose to go minus a scholarship despite his obvious golfing talents.
"They didn't offer me, but I wanted the fraternity life," he says.
"I was actually recruited for basketball but I was too short and too slow for that."
Ohio State certainly benefited from his golfing talent, winning two U.S. Amateur titles and the NCAA Championships in 1961.
He was already earmarked for professional stardom, and in his first full year on the PGA Tour he captured his first major at the 1962 U.S. Open, beating the crowd favorite Palmer in a playoff.
A staggering 17 more major titles followed, his last memorably at the age of 46 in the 1986 Masters when he became Augusta's oldest winner.
It was an unlikely triumph, with young stars such as Greg Norman and Seve Ballesteros thwarted by a true golfing legend.
Golf fan Milstein watched it all unfold on television, and now understands the special qualities possessed by his partner.
"When Jack got close to winning, he would win -- he started putting it together under pressure, and that's what counts."
Nicklaus made an emotional final appearance in the 2005 British Open at St. Andrews and famously signed off with a birdie on the 18th, holing a tricky putt with the world watching.
Milstein asked him if he had been nervous at the moment. "He told me, 'It never occurred to me it would not go in,' and that's part of his magic -- supreme confidence."
Nicklaus' public appearances on the course are now largely limited to his role of honorary starter at the Masters with Palmer and Player, but it did not stop him from carding the 21st hole in one of his career in the 2015 par-three tournament -- his first ace at Augusta.
His all-time record of 18 majors looks set to stand for many a long year, particularly with the recent travails of his nearest rival, Tiger Woods, who has been stuck on 14 since 2008.
Nicklaus still believes Woods has a shot at his record despite his recent injury problems, but believes the game is in "good hands" with the likes of Jordan Spieth and Rory McIlroy at the top of the rankings.
Nicklaus travels extensively, including regular trips to China where he has 18 golf design projects under development, but is frustrated by the sluggish growth of the game in a country with incredible potential.
"We need help from the Chinese government. It's a bit of a 'wait and see' but having golf in the Olympics (in Rio 2016) will help," he says.
If gold medals had been handed out during Nicklaus' playing career, it's a safe bet he would have stood at the top of the podium more than once, given his domination of the world game for so many years.
And according to Milstein, nice guys really do come first.
"Jack is the most genuine and most wholesome and straightforward and successful American that you will find," he says.
"Those are great attributes in a partner, and he is good to his word."