Two of these are likely to be competing in the equestrian disciplines: one is the British dressage rider Charlotte Dujardin; the other is Michael Jung, the German three-day eventer.

I caught up with Jung, who has so far won three Olympic gold medals in all, by telephone last week a couple of days after his 37th birthday and less than a week after the shock announcement that doyen of the sport Sir Mark Todd was retiring from eventing.

Jung confesses he was also surprised.

"When he is riding it looks so perfect – smooth and with such good balance," he says of Todd.

"He is a great man, not just a great rider – friendly and open," he adds.

"Of course" it should be easier to win in Tokyo knowing that the New Zealander will not now be there, Jung acknowledges – "but there are a lot of other strong competitors".

Mentioning Todd and Jung in the same breath is appropriate: not only are they two of just three athletes – the other being Charles Pahud de Mortanges of The Netherlands – who have won the individual eventing title at two consecutive Olympics; both have also competed to a high level in another equestrian discipline – jumping.

Todd, indeed, took part in both eventing and jumping at the Seoul 1988 and Barcelona 1992 Olympics.

"I like to change," says Jung, who was recently part of the German team at the Jumping Nations Cup event in Hickstead, southern England.

"I did it from the beginning at low level," he explains.

"I have a lot of young horses…

"We do not have many eventing competitions, so for me it is perfect to do something else."

He downplays any suggestion that he might seek to emulate Todd by competing in both disciplines at Tokyo, however.

"I think it is possible, but very difficult on this level," he tells me.

"It is still a dream for me to compete once in a championship in jumping."

But not in Tokyo?

"I don't think so."

While equestrian riders can remain at the top of the sport for many years, this is less true of their mounts.

Just like Dujardin, accordingly, if Jung is to register a remarkable Olympic hat-trick, it will be with a new horse.

Sam, who carried him to his two individual gold medals in London and Rio, is now retired, Jung tells me, though "I will keep him".

Expectations are currently that his partner in Tokyo is likely to be an 11-year-old bay gelding called Chipmunk (actually fischerChipmunk FHR), which had been ridden for six years by Julia Krajewski, a German team-mate of Jung's in Rio.

Jung and Chipmunk – who led the field with Krajewski in the saddle after the dressage leg of the eventing competition at last year's World Equestrian Games in North Carolina – will probably be among the favourites to win the European Championships at Luhmühlen in Germany later this month.

For now the rider, whose base is near Stuttgart in southern Germany, is slightly hedging his bets, saying it is "not 100 per cent sure" that Chipmunk will be his next Olympic horse.

He describes him nonetheless as "a super horse with some experience, super in all three phases".

Before Luhmühlen, Jung – though not Chipmunk – is off to Japan for the Tokyo 2020 equestrian test event from August 12 to 14 at the brand new Sea Forest venue.

The German says he is "very looking forward to seeing the facilities" and that he thinks Tokyo 2020 will be a "very nice Games".

His use of a younger horse for the test event is explained, he says, because it is a "medium-level" competition.

Horses are very much in Jung's blood: his father, Joachim, competed at elite level; Jung himself started riding at four and competing at eight.

His first pony, he tells me, was called Sally.

He adds: "I hope to continue as long as [63-year-old] Mark Todd."

The sport does have its hardships, however: Jung's biography page on the International Equestrian Federation website includes a broken collar-bone, a broken arm, sustained in October last year, and a chipped tibia that required two screws to be inserted in a subsequent operation.

Since the Second World War, equestrianism's Olympic presence has been remarkably stable, comprising six events – three individual, three team – with the sole exception of Rome 1960, when there was no team dressage.

Competition among sports for the best possible slice of the Olympic pie is intense, however, and with the International Olympic Committee moving to an event-based assessment of the Games programme, one wonders whether these days of stability are threatened.

When I ask Jung about the security of his sport’s Olympic place, he is candid enough to acknowledge that "I think it is always a bit on the borderline".

He goes on, however: "I think it is a nice sport.

"I hope it will always be in the Olympics."

Finally, with the UK and marquee events such as Badminton and Burghley so important for the sport of eventing, I feel I must ask Jung if he is concerned about any impact Brexit might have.

"I think it will be much more difficult," he says.