By Frank Pingue

(Reuters) - San Antonio Spurs stalwart Tim Duncan, a model of consistency during an illustrious career during which he won five NBA championships and established himself as the game's greatest power forward, is calling it a career.

Weeks of speculation about Duncan's playing future came to an end on Monday as the Spurs said the 40-year-old face of the franchise was retiring after 19 NBA seasons spent entirely with the small market San Antonio franchise.

The towering figure was selected first overall in the 1997 NBA Draft and went on to turn the Spurs franchise into one of the best in North American sports for nearly two decades.

Duncan, whose longevity was virtually unmatched, was a force on both ends of the court while racking up numerous individual awards that will ensure he is inducted into the Basketball Hall of Fame in his first year of eligibility.

"For two decades Tim represented the Spurs, the city of San Antonio and the league with passion and class," NBA Commissioner Adam Silver said in a statement. "All of us in the NBA family thank him for his profound impact on the game."

Duncan, who was born and raised in the Virgin Islands, was a relative latecomer to the sport of basketball. His first love was swimming but he turned to basketball when a hurricane destroyed the only Olympic-sized pool on his island.

Prior to the NBA, Duncan enjoyed a successful career at Wake Forest University in North Carolina. He was named U.S. college basketball's top defensive player three times and Player of the Year in his final season before entering the 1997 NBA Draft.

He went on scale the heights of the NBA where he helped San Antonio reach the playoffs in each of his 19 seasons and became the only player in league history to start and win a title in three different decades.

Duncan, who was the league's rookie of the year in 1998 and twice named the NBA's Most Valuable Player, finishes his career as the Spurs' leader in total points, rebounds, blocked shots, minutes and games played.

"Even tho I knew it was coming, I'm still moved by the news. What a HUGE honor to have played with him for 14 seasons! #ThankYouTD," tweeted Spurs guard Manu Ginobili, who together with Duncan and Tony Parker made up on the NBA's most dominant Big Three.

The Spurs had the NBA's second-best record in the 2015-16 season but lost in the Western Conference semi-final, after which Duncan said he was contemplating his playing future.

He averaged 19 points and 10.8 rebounds during his career and retires as one of three NBA players along with John Stockton and Kobe Bryant to spend 19 seasons with one franchise.

(Reporting by Frank Pingue in Toronto; Additional reporting by Shravanth Vijayakumar in Bengaluru; Editing by Alan Baldwin and Andrew Both)