Callander, who had pancreatic cancer, was a combative hooker who excelled at sevens, and was capped six times.
He made his international debut in the defeat by Romania in Bucharest in 1984 and had to wait four years for his second cap. On that occasion, against Ireland in the 1988 Five Nations, he captained Scotland, an honour bestowed on him for the remainder of his appearances for the national side.
The most memorable of those was a 24-11 win over France at Murrayfield in 1988.
He was part of a superb Kelso side who were champions of Scotland two years running, in 1987-88 and 1988-89, captaining them to the title in the former. He also led them to their first Border League triumph in 50 years in 1985-86.
If the Poynder Park side were dominant in 15s for a period, they were almost unstoppable at sevens and Callander won five Melrose winners’ medals with the club.
Scott Forbes, the president of Kelso, said: “Gary’s contribution to the history of the club cannot be overstated.
“He was a captain, leader and an outstanding rugby player. He will be sorely missed by his ‘rugby family’. Our thoughts are with Gary’s family and friends at this sad and difficult time. May he rest in peace.”
Scott Hastings, the 1990 Grand Slam hero who played alongside Callander in the 1988 Five Nations, said on Twitter: “Gary was fiercely passionate but utterly driven. A great tourist and a man who loved his rugby.”