Ramsey's death was announced by Kentucky, where he was part of the Wildcats' 1951 national championship team and a three-time All-American. The school said he died of natural causes.
The 6-foot-3 guard was selected by the Celtics in the first round of the 1953 NBA draft and began his professional career one year later. He averaged double figures in eight of his nine seasons and 13.4 points per game for his career. His No. 23 jersey is retired by Boston.
The Celtics said in a statement that the "original sixth man" helped create a legacy of excellence and selflessness that "remains part of the Boston Celtics ethos to this day."
I am in shock & deeply saddened to hear of my long time friend & teammate #FrankRamsey passing I had the great pleasure to speak with him often. He won 7 @NBA & 1 @NCAA title & was the 1st true 6th man. He was a great man & father. I will miss him! @celtics @KentuckyMBB @espn pic.twitter.com/X166yw76PD— TheBillRussell (@RealBillRussell) July 8, 2018
Ramsey, 86, went on to coach the Kentucky Colonels in the American Basketball Association for a season and later served on the Kentucky Board of Trustees.
He was elected to the Naismith Memorial Basketball Hall of Fame in 1981.
Hall of Famer Bob Cousy said he spoke with Ramsey, his friend and former teammate, regularly and last talked with him about a month ago.
"He might as well have been the mayor of Madisonville, Kentucky,'' Cousy told ESPN. "He was president of the bank. He owned a general store. I said to him, 'Rams, you've got more money than Trump. Why don't you retire?' He told me, 'No. I love this. I'm not on meds, I feel great. I want to keep going.' That's why I'm so sad and surprised to hear [of his passing]."
Ramsey was the sixth man on those early Celtics championship teams. Cousy claims he could have been a starter, but, he said, "for some reason Arnold [Auerbach] used him off the bench to re-energize our group. He was one of those players who made things happen, so I guess Arnold read it correctly.''
Asked to describe Ramsey's game, Cousy said, "He was instant activity. He could score, play excellent defense and was a good rebounder for his size. He was truly an all-purpose player.''
It turns out Ramsey was also the team's resident practical joker. He was a stickler for being on time, and he often came to practice early to play tricks on big man Tommy Heinsohn, who often arrived at the workout facility with little margin for error.
"We all knew this about Tommy, but Rams would arrive early and tie Tommy's shoes together,'' Cousy recalled. "Arnold would fine us $1 per every minute we were late, so when Tommy came running in just as practice was about to start, he'd wind up being late anyway because his shoes were tied in knots.''
Information from The Associated Press and ESPN's Jackie MacMullan was used in this report.