ON TUESDAY John Magnier will be able to relax as he settles into Cheltenham for the three-day National Hunt festival where he will watch his son, JP, go for the Coral Cup on Rhinestone Cowboy.

The Irish millionaire’s fight with Manchester United manager Sir Alex Ferguson over ownership of the prize-winning stallion Rock of Gibraltar is over.

Magnier won — and humiliated Ferguson, who had to back down from claiming half-ownership of the £40m horse and settle for £2.5m.

In the course of his battle with Ferguson, Magnier and JP McManus, another Irish millionaire, increased their ownership of Manchester United to 28.9%, cementing their position as the largest shareholders in the world’s largest sports franchise.

“Magnier expects his representative to be welcomed onto the club’s board soon after the March 30 annual results,” an adviser said.

Magnier’s eight months in the headlines have made him controversial. His scorched-earth tactics in the fight against Ferguson, including the employment of Kroll to investigate his adversary, have reinforced the impression that he is part of an Irish business mafia.

With a net worth of £500m, Magnier flits in private jets from Coolmore Stud, his lush horse farm in Co Tipperary, to Barbados, where he has a residence and a share in the £500-a-night Sandy Lane Hotel, to his house in Verbier, Switzerland, where he will be skiing this Easter.

But Magnier’s fight with Ferguson also served as an announcement — there is a new star in the Anglo-Irish firmament. Magnier has taken his place alongside other pretenders to the Sir James Goldsmith crown for having the most assets at home and the most tax addresses abroad.

Magnier’s tale — it is one of rags to riches — revolves around spotting an opportunity, overcoming a shortage of capital to exploit it and using new technology to do so.

Today Magnier dominates the global horse-breeding industry he helped to invent. “John Magnier is the Bill Gates of the horse world,” said Bill Oppenheim, a bloodstock entrepreneur and consultant.

Because he has emerged through equine capitals such as Newmarket and Kentucky rather than financial ones, his rise is particularly colourful. Magnier’s top stallion, Sadler’s Wells, has attracted business from the Aga Khan, songsmith Lord Lloyd Webber and the Queen. All have sent mares to be impregnated by the prize-winning thoroughbred.

In an age when the path to commercial power typically intersects with giant companies such as BP or Goldman Sachs, Magnier has remained a sole trader. He has little formal education and he remains true to his Irish country roots. “Why did Magnier fight Ferguson?” asked an associate. “Simple. The way it was seen, it was like stealing a horse.” In the Irish countryside you don’t do that.

The nation into which Magnier was born in 1948 on Grange Stud in Fermoy, Co Cork, was not only rural, but also still adjusting to independence 28 years earlier. America was a mystical emigrant destination, but the post-war strategies being developed by American companies to dominate world markets seemed as remote and unfathomable as the mysteries of the Catholic faith.