Obsessions, by definition, are curious things.

Lloyd Williams has one, and it is, indeed, curious.

For more than 30 years, Williams has devoted himself to winning Melbourne Cups.

And while he's not in the Bart Cummings class, he's been good at it.

Four wins since 1981, including Tuesday's with Green Moon, is a record only Cummings and Lee Freedman have improved on.

But Williams has probably gone to more extraordinary lengths than either of them to win Australia's greatest race.

From the late 1990s he did his best to corner the market in the stock of the wonderful New Zealand-based stallion Zabeel.

Williams regularly had dozens of them running around on his farm and in his stables.

Mostly the Zabeel experiment was folly, although it produced Efficient, Williams' third Cup winner in 2007, the Sydney Cup winner Gallic and the unbeaten racehorse and successful sire, Reset.

In the beginning Williams employed public trainers to prepare his horses.

Tommy Smith trained his first Cup winner Just A Dash in 1981 and John Meagher trained 1985 winner What A Nuisance.

By the time of Efficient's win he was employing private trainers - and regularly un-employing them.

Graeme Rogerson, who accepted Efficient's Cup trophy, was his third trainer in five years, and he's had two more since then.

Along the way, Williams, whose vision for grand projects is best demonstrated in Melbourne's Crown casino which he built in the early 1990s, bought a training complex north of Melbourne where his team is trained in privacy and luxury.

With Zabeel now a pensioner, Williams has turned to Europe to indulge his Melbourne Cup preoccupation, becoming something of an authority on northern hemisphere bloodstock.

Green Moon is an Irish-bred horse who raced with moderate success in England where he won three races.

He's one of 20 horses Williams has bought in Europe in what he describes as his "latest phase" of purchases.

But he has signalled that a new era might not be far away.

"A lot of people are going to burn their fingers buying these horses," he said.

"I speak from experience. From 1986 to 1990 Kerry Packer and I bought 42 of these horses, and they weren't that good.

"It's the flavour of the month to go out and buy an English horse, but I'll tell you what, the people over there are rubbing their hands together with glee."

Over here, Williams is doing the same.

But on Tuesday he wasn't doing it from the stands at Flemington.

As he did when Efficient won, Williams cheered Green Moon to the line from his farm at Mt Macedon, preferring to stay away from Flemington.

For a man who has spent many, many millions on his obsession with the Melbourne Cup, that seems particularly curious.