It was the summer of 2000, and Duncan, future Hall of Famer for the San Antonio Spurs, was making a free-agent trip to another city. By all accounts, Duncan was seriously contemplating the Orlando Magic. He was 24 years old, his eyes were even bigger than they get when he is called for a questionable foul, and Orlando was wooing him and Grant Hill to change the face of a franchise.

Back in Texas, a man with a gruff exterior and a social-studies-teacher wardrobe was helpless. Spurs coach Gregg Popovich probably wouldn't have admitted then that he had really grown attached to that kid. It wasn't just that Duncan was 7 feet tall and did things so effortlessly. Duncan and Popovich had become soul mates. They were complete opposites. Popovich was a connoisseur of fine wine; Duncan drank soda. Duncan played video games; Popovich barely knew how to turn on a computer.

Duncan did not plan a TV show to announce his intentions. He went home to San Antonio, and the same questions kept floating through his head. What are you doing? Why would you mess with something so great?

Tim Duncan and Gregg Popovich have been together for 16 years, and it's the greatest love story in sports. They collaborate and lean on each other, win championships together, then comfortably fade into the anonymity of the NBA's third-smallest TV market.

It's not a love full of hyperbole or flowery prose. Duncan and Popovich have this game-day ritual. Popovich takes a seat on the bench alone at halftime, while the rest of the arena is scrambling or shooting or going for a beer, and then Duncan plops down near him. They stare at the ground. Usually, they say nothing. They've been doing this for years, and everyone has different theories as to why.

"They both are probably thinking the same thing," said New Orleans Pelicans coach Monty Williams, who played with Duncan his rookie year. "Whatever that is, I don't know."

"Pop is old and so is Tim, and they both need to get their rest," former Spurs guard Brent Barry joked, then offered a more serious explanation.

"You have two sets of eyes on you as you're finishing off the task at hand. You have the coach, but then you have the coach's first son. Your older brother. Kind of the man of the house with Dad's car. And Tim is watching over and kind of quietly assessing what you're doing, and nothing really needs to be said."

Duncan and Popovich have won four titles together in 16 years and are in a tug-of-war with the Miami Heat for No. 5. They are so bonded that Popovich said earlier this spring that he'll retire when Duncan does.

No player and coach in the history of the NBA, or even the NFL, have been together longer. New England Patriots quarterback Tom Brady, who has teamed up with Bill Belichick for one of the biggest dynasties in football, was just a sophomore backup at the University of Michigan when Duncan and Popovich got together. Phil Jackson was winding down an eight-year run with Michael Jordan. "I think it speaks to the character of both of them," Jackson said of Duncan and Popovich's longevity.

Their relationship has been called everything from friendship to father-son to a marriage. Neither is interested in analyzing it, especially now, in the final push for another ring.

But they're intensely private men anyway, which makes it tough to fill news cycles in San Antonio. One local TV station was so desperate it recently ran a slideshow on its website of pets wearing Spurs gear. (The lapdogs and kittens were more revealing than Popovich.) Just before the NBA Finals started, the coach was asked to give his first impressions of when he met Duncan. "He was tall," Popovich said, then walked away.

Perhaps if they opened up more, they would reveal secrets they don't want anyone to know. Such as that their chemistry makes everything seem easy.

Gregg Popovich is known as a coach who inspires selfless team play. D. Clarke Evans/Getty Images

It has been said that Tim Duncan was so agreeable, so good, that he could've been coached by anybody. He had long arms, a beautiful bank shot and a toughness that belied his sinewy frame. There was a purity and genuineness about him, almost as though he'd been untouched by the entitlements that come to someone who knows at a young age that he's better than everyone else.

Duncan was. He grew up in the U.S. Virgin Islands. His coach, apparently, was a chemistry teacher. He might never have gotten noticed had an ex-Wake Forest player not played against him during an NBA rookie tour of the Caribbean and had that player's coach not been a constant recruiter, always asking, "Did you see anybody good?"

Duncan had four schools after him -- Wake Forest, Delaware State, Hartford and Providence -- and loathed cold weather. It snowed when he visited Hartford and Providence.

"The recruiting process was not, shall we say, sexy from there," former Wake Forest coach Dave Odom said.

So Wake Forest it was. Duncan's biggest influence, Odom said, wasn't a coach. It was his family. He grew up around women, around two older sisters, with a father who built their house with his own hands. His mom, Ione, was probably his most passionate supporter. "Good, better, best, never let it rest," she used to tell Tim. She died before his 14th birthday. When he was projected to go high in the NBA draft as an underclassman, he stayed to get his degree because that's what he had promised his mom.

San Antonio selected Tim Duncan with the No. 1 pick of the 1997 NBA draft. Craig Jones/Getty Images

In Duncan's final home game at Wake Forest, the school retired his jersey. The place was packed, and when Odom addressed the crowd at the end of the game, Duncan's dad, William, asked whether he could speak. He thanked Wake Forest for being so nice to his Timmy. He repeated part of the mantra Ione used to tell her kids.

"And with that," Odom said, "Tim Duncan wrapped his arms over his dad from behind and didn't let him say anything more."

Duncan, who eventually earned the ho-hum nickname "The Big Fundamental," always had simple needs. In the days before the 1997 draft, he was not consumed with his potential salary or thoughts of landing in a big city. He just really wanted to live somewhere warm. The Boston Celtics had a 36 percent chance of landing him, and Duncan, according to Odom, wasn't too thrilled about that.

Out in San Antonio, Popovich was in his first season as an NBA head coach, and things were downright miserable. The Spurs' star, David Robinson, was out with back and foot injuries. Popovich went 17-47. But his luck was about to change.

The ping pong balls bounced San Antonio's way that summer, and the Spurs earned the No. 1 pick. They would get Duncan, and would have Robinson back the next season. With two 7-foot superstars, they'd be the envy of the NBA. But Popovich still wanted to do his research. He flew to St. Croix before the draft to spend a few days with Duncan in his environment.

Had the trip gone bad, it probably wouldn't have mattered. The Spurs were going to draft Duncan regardless, general manager R.C. Buford said. Popovich went to lay the groundwork. He's big on building relationships. He wants to know his players outside of the gym.

Duncan and Popovich swam and had long talks. They realized how much they had in common. It wasn't about Popovich pretending to be knowledgeable about in-line skating or paintball -- Duncan is so competitive in paintball that teammates say he used to arm them with crooked guns -- or Duncan pretending to like subtitled movies. It was deeper than that.

"They have a burning passion to win and win championships," said Phoenix Suns exec Lon Babby, Duncan's former agent. "That isn't so unusual. What separates them is the way they go about their business without any distractions, without any noise.

"They're both blunt, they're both direct. They're singularly focused and not distracted by the business of the NBA."

There's chemistry among Gregg Popovich and his players. Andrew D. Bernstein/NBAE/Getty Images

It has been said that Popovich can coach anybody. His teams are selfless and quiet and consistent and, well, boring to the rest of the NBA. His players constantly seek his approval, even after they've left San Antonio. One-sixth of the head-coaching jobs in the NBA next season will be filled by men who used to play for or coach alongside Popovich.

All of them call him "Pop." They insist he's not the curmudgeon on display in the media. He can chew a player out at noon and by 6 o'clock is on the phone with that player, inviting him to a new restaurant in town. Popovich always insists on picking up the check, no matter how many zeros there are in his guest's salary. When the team travels to Washington, D.C., Pop will take it on a trip to the Pentagon.

Years ago, there was a strength and conditioning coach -- an intern, apparently -- who decided to become a youth minister. The guy didn't have much money, so imagine his surprise when he received a going-away gift, a Nissan Pathfinder, courtesy of Popovich. "Pop would probably kill me right now if he knew I was talking about this," said Cleveland Cavaliers coach Mike Brown, a former Spurs assistant who witnessed the deed. "He's done a million things like that."

Popovich's need for secrecy is a product of his younger days. He went to the Air Force Academy, majored in Soviet studies, and underwent intelligence gathering and processing training. He contemplated a career with the CIA.

But beyond that training, Popovich just doesn't have time, or patience, for the things he doesn't deem important. He is sentimental and values friendships. He has love for anyone who competes. When someone doesn't, that's when Popovich goes off on a rant. The tirade might last only 10 seconds, but it feels like 10 hours. Popovich doesn't discriminate, either.

Brown saw Popovich once rip into a player in front of God, the TV cameras and the entire team during a game. The player was Duncan.

They have grown so close that Gregg Popovich, 64, has said he'll retire when Tim Duncan, 37, does. USA TODAY Sports

"He calls timeout, grabs a chair, puts it right in front of Tim and just goes after him," Brown said. "And I'm sitting there thinking, 'OK, I just got here, this is my first year. I really don't want to move again, but it looks like we're going to end up moving again. Because I will no longer have a job after this game.'

"Your perception is that if you go after your superstar like that in front of everybody, you think there's going to be a strained relationship between the coach and the best player. And it was far from it. With the rest of the guys watching Pop coach the way he did, they knew that, Hey, if you're the third-best player or the seventh-best player, you'd better be able to take it because the No. 1 player on the team did, and he took it like a pro."

Duncan takes it because he knows every rant goes a long way with the younger players. It takes pressure off them. Duncan trusts Popovich. He used to tell former Spur Bruce Bowen, an ESPN NBA analyst, that Popovich came down on the players he knew could handle it. "He's not going to show favoritism over someone," Bowen said.

Possibly the first guy to consistently get on Popovich's bad side was Monty Williams. He was a young and rebellious player back in 1997 and often didn't get why Popovich was always yelling at him. The veterans tried to explain that it meant Popovich liked him. Williams didn't see it.

He made stops at three other teams after San Antonio, injured his knee, and one day was told by Dr. James Andrews that his playing career was over. Upon hearing the news, he called two people: his wife and Gregg Popovich. He has no idea why he felt compelled to call Popovich.

The coach suggested he come to the Spurs' practices and watch, and he took notes for three months. Popovich kept giving him more responsibilities. In 2005, he was an intern assistant when the Spurs won their third title. As the team celebrated, Williams stood off to the side and watched.

Someone grabbed him from behind and gave him a bear hug. It was Popovich. "You got one," the coach said. He watched Popovich the whole series, how he was undaunted after a Game 6 loss, when the Spurs were counted out, how he stayed up all night figuring out how to beat the Detroit Pistons in Game 7.

After the season, Popovich met with Williams and asked what he wanted to do. He could get into management. He could coach.

Williams looked at him and said, "Pop, I want to be like you."

Popovich nodded and walked away.

"I think the general level of caring that he displays is not normal," said Atlanta Hawks general manager Danny Ferry, who used to play for Popovich. "But he cares about the world around him, and he cares about the people he's with very much."

After every season, Brown says, Popovich thanks Duncan for allowing him to coach him. They do charity work together. Earlier this year, Popovich and Duncan helped with a fundraiser to raffle off a custom-made Spurs truck for the San Antonio food bank. Duncan, who recently opened a custom-car shop in San Antonio, actually designed the tricked-out truck, which was won by a single mother who was driving a worn-out minivan from the 1990s.

Popovich is always low-key about his charity work, said Eric Cooper, president and CEO of the food bank. He won't tell him when or where he'll visit because he doesn't want cameras there. "If I ever tried to recognize Pop for an award or something," Cooper said, "I think he would punch me."

"They have a burning passion to win and win championships," said Phoenix Suns exec Lon Babby, Tim Duncan's former agent. Kyle Terada/USA TODAY Sports

But he'll put his arm around Cooper and tell him he's doing good work.

Duncan and Popovich did a photo shoot to help promote the fundraiser. Duncan cracked a joke about Popovich's wardrobe, but for the most part, they were quiet and rushed to get back to work.

The fact that Duncan can still sprint is impressive. He's 37 now and, before the 2012-13 season, appeared to be -- like the minivan -- closing in on his final miles. But he lost 15 pounds in the offseason, which took pressure off his knees and boosted his production. Duncan averaged 17.8 points and 9.9 rebounds this season, and he has 11.2 rebounds a game during the NBA Finals. Two years ago, he averaged 13.4 points and 8.9 rebounds.

Popovich has helped. He has rested Duncan on road trips, occasionally filling in the lineup with the explanation of Duncan's absence as DNP--Old.

Years ago, sometime after Duncan turned 30, he told his agent he was starting to worry about when he wouldn't be able to play the game anymore. He was worried because he loved it so much. He never saw the NBA as a springboard for a brand or a second career. Duncan left millions on the table in endorsements, Lon Babby said. He immediately said no to 98 percent of the offers, and in the 2 percent that seemed to make sense, he'd tell Popovich about it, then Pop would ask why he's wasting his time with it, and that would usually be the end of it.

"They bring out the best in each other and complete each other so well," said former NBA coach P.J. Carlesimo, "that you're tempted to say it's the perfect relationship. I don't think there is such a thing. But it would be hard to find one much better."

It's not perfect. In the frustration of Thursday night's 109-93 Spurs loss to the Heat, Popovich unloaded on Duncan, who took a seat on the scorer's table while Popovich huddled with the team. By halftime, though, it appeared they had made up. They sat together on the bench, and Popovich slapped Duncan's knee. The end of the conversation, without volume, was caught by the ABC cameras.

"I'm not mad," Popovich appeared to tell Duncan.

They have been together through 16 playoffs and hundreds of road trips. They have been through death and now divorce. Popovich, who is 64, has known Duncan for his entire adult life, before Duncan and his wife, Amy, had two kids. They were in the middle of the Western Conference finals against Memphis last month when the San Antonio Express-News broke the story that Tim and Amy were getting divorced.

Duncan was unflappable. He led the Spurs to a 4-0 sweep of the Grizzlies. He'll deal with his personal life when the season is over. No one knows how this season will end. Or when Duncan's body will tell him he has had enough of basketball. When it does, Duncan likely will focus on his cars, and Popovich will sip his wine.

Sometimes, when Duncan is struggling, he'll go to Popovich's house, late at night, to talk. Regardless of basketball, that won't end, people close to them say. That family will remain intact.

"When you talk to Pop," Monty Williams said, "basketball is, especially in the offseason, like 20 percent of the conversation. I mean, Pop and I are friends. Just imagine how close he and Tim are.

"I don't see how the game of basketball will bring an end to that. I think those guys will be friends until they're dead."