A 2006 photo of a gathering of the five fastest Australian marathoners of all time (from left): Derek Clayton, Robert de Castella, Pat Carroll, Steve Moneghetti and Lee Troop (© Adam Head)
But there was a period when the tall Melbourne runner was the world's fastest over the classic road distance of 26 miles 385 yards or 42.195km.
In fact he held the world record for 12 years until 1981 when another Aussie, Rob de Castella, took over.
Clayton, 66, was the first man to run under 2hr 10min when he ran his first world record of 2:09:36.4 in Fukuoka, Japan on December 3, 1967. Japan's Morio Shigematsu had the best on record until then with his 2:12.00 in Chiswick, England on June 12, 1965.
Then in Antwerp, Belgium, Clayton lowered his own world best to 2:08:33.6 on May 30, 1969 - the first to crack the 2:09 barrier and more than two minutes faster than history's next quickest, Britain's Bill Adcocks (2:10.47.8) run in 1968.
It was such a stupendous breakthrough that sceptics throughout the following decade would speculate that the course must have been short.
Yet only 11 days before his historic run in Belgium, Clayton ran at high altitude and won a marathon in Ankara, Turkey on 19th May, in 2:17.26.
“I had to run faster than I'd planned. If I hadn't run in Turkey I would have run 2:07 in Antwerp," Clayton told The Daily Telegraph this week.
Forty years on though the Africans have advanced the record, Ethiopia's Haile Gebrselassie running 2:03:59 in Berlin last year.
And still we ask, will we ever see a man run faster than 2hrs in a marathon?
“I was asked that the first time 40 years ago," Clayton said. “I'll give you the answer I gave all those years ago: I won't see it in my lifetime.
250 miles per week during build up
“Gee whiz. I don't know. It's getting pretty quick. I still don't know if I'll see a 2hr marathon because these guys, none of them are training any harder than me. I can say that for a fact."
Really? Gebrselassie ran 250km (156 miles) a week during his buildup to Berlin. Well, Clayton ran 250 miles a week.
“It was all experiment," he says now. “I didn't have books or magazines back in my day. I was flying blind.
“No-one had done what I did. There was no-one to talk to. No-one knew anything much about marathon running, had a lot of experts on 1500m and 5000m but not on marathon running. I was a bit of a pioneer.
“I was shooting in the dark a bit, so I tried 250 miles a week later in 1969.
“I just wanted to see how my body accepted it - and that was not very well, only because I started getting injuries.
“I did some miles before Antwerp because I wanted to run under 2:08. I used to have a typical buildup of 10 to 12 weeks before a marathon because I felt if I pushed it much more than that I was going to get injured or sick.
“Before Antwerp I probably averaged 170 to 180 miles per week.
“A lot of it was quality. I thought the quality part was the important part. A lot of people could run 180 miles if you run it slow enough, but I wanted to maintain a high rhythm, in the rhythm of the race. I wouldn't start off hard. I'd start off at a leisurely pace and then build-up, but I'd finish off pretty quick."
A lot of those miles, certainly in the early years leading up to his world record in Fukuoka, were run in the original Dunlop volley tennis shoes which had soft canvas uppers so his feet didn't blister on top. But they had precious little support beneath the foot compared to today's top training shoes.
“The difference [in the depth as well as quality of marathon running now] is in the shoes they are wearing and the fact that they've got many opportunities to run a fast one because you've got a thing in track and field now that I'm dead set against: Pacemakers," Clayton said.
“It is ruining track and field. It is ruining it for Australians because it [athletics] is about racing, it's not about times."
Mike Hurst for the IAAF