The 58-Test lock debuted against South Africa in 1981 and was a member of the 1987 Rugby World Cup-winning All Blacks.
Having played soccer for much of his youth, it was at Auckland Grammar in the fifth form where he and his twin Alan started playing social rugby.
His science teacher and 1st XV coach Graham Henry told him that if he put his mind to it, Whetton could do well in rugby. He went on to have two seasons with the 1st XV.
"He said, 'You've got to put your mind to it. You've got all the attributes, the athleticism, all that. You've got to get yourself right, your mind, get fit, and we'll see where we can take you.'"
Whetton said he still wasn't performing at his best when leaving school after the seventh form. Alan had played representative rugby, but he hadn't and said that was because he was lazy.
However, Henry said to him, "You know Gary, of all the players here you can be an All Black if you put your mind to it."
Getting a job at Fisher and Paykel provided the inspiration that turned things around for Whetton. He continued playing rugby with the Grammar Old Boys' third-grade side, and had played some representative rugby without setting the world on fire.
The company told him they were sending him on a three-and-a-half-week stint at Outward Bound.
"I didn't know what it was all about. I hated it for the first two weeks.
"The last week and a half, I worked it all out, came back. I was a stone and a half lighter [9.5kgs]. My parents and everyone said, 'You've changed'. My whole attitude had changed. Outward Bound did a lot for me," he said.
Progress through the rugby ranks reflected that change as he played two seasons for the New Zealand Colts and then made his debut in the third Test against South Africa in 1981.