Since being employed full-time by Rowing New Zealand in 1999, his charges have picked up a gold medal at every Olympics. He helped make household names of Rob Waddell, Caroline and Georgina Evers-Swindell, Mahe Drysdale, Hamish Bond and Eric Murray.
Tonks' methods are beyond dispute. Perhaps the most telling statistic is the 68 Olympic or world championship medals (35 gold, 16 silver, 17 bronze) New Zealand rowers have won since the 2004 Athens Games.
Pre-2004, there were seven Tonks-driven world championships (shared between Philippa Baker, Brenda Lawson, Waddell and the Evers-Swindells) and two Olympic titles (Waddell and the Evers-Swindells) to cement the 64-year-old's authority in the rowing ranks.
The cumulative effect over the years is that rowing is High Performance Sport New Zealand's top funded sport - last week $5.3 million was set aside for investment next year.
Tonks' reputation as a hard task-master is countered by the fact he is the most successful coach in New Zealand Olympic history. He has been the Halberg coach of the year five times (1999, 04, 05, 09, 12).
But that looks set to change if, in his own words, he is indeed "finished" with Rowing New Zealand.
Tonks had been working with Chinese men's rowers on Lake Karapiro, the same training base of New Zealand's crews, but decided to move on when his link was questioned by the governing body.
A final decision is due by lunchtime. Essentially it seems the master coach felt his integrity built over more than 20 years coaching at elite level was ignored, while the governing body believed their security protocols around Rio intelligence were breached.
The relationship looks set for a clean break unless a diplomat of Mandela-proportions can be rustled up in a hurry. Waddell, in his role as chef de mission and as a former Tonks charge, is one of the few with the requisite skills to intervene.
For Tonks this is the latest in a series of difficulties with the governing body. He took a new role as head of the women's rather than the overall programme after the London Olympics after mentoring Drysdale, Hamish Bond and Eric Murray to gold medals. Last season he coached Drysdale and the women's double of Stevenson and Macfarlane.
For Rowing New Zealand they must be seen to take a stand, or at least initiate a dialogue, against any threat to their intellectual property. As insurance for a crisis like this they have built a succession plan of coaches capable of securing multiple world championship (Gary Hay and Dave Thompson) and Olympic medals (Noel Donaldson and Calvin Ferguson).
