The then state-owned Telecom Eireann didn’t know what hit it as Esat ate its lunch and grew rapidly.

BT bought the firm for €2.4bn in 2000, with O’Brien netting an estimated €317m from his stake. Spotting an ad in the FT that Jamaica was deregulating its telecoms market and selling a mobile licence, he decided to replicate Esat in the Caribbean, buying the licence for around $57m. Since then, his Digicel group has mushroomed, with over 14 million customers in 30 countries from Central America to the Pacific. The group, which had revenues of more than €2.1bn last year, is worth around €8.1bn. Dublin-born O’Brien (56) owns 94pc.

There’s also approximately €5.3bn in debt, with almost €1bn raised last March. O’Brien has taken some money off the table with an estimated €1.57bn paid out or due to be paid out in dividends in the last seven years, including a €546m payout pencilled in for last year. Weak local currencies, virtual operators such as Viber and increased competition have made life a little tougher over the last year.

Despite missing out on a lucrative mobile licence in Burma, O’Brien is busy building mobile masts in the country. Elsewhere, Digicel is actively looking at new markets and opportunities including the rollout of cash transfer using mobile phones.

O’Brien has invested his fortune widely, with Forbes estimating his worth at €5.97bn. He owns a 29pc stake in INM, publisher of the Sunday Independent, and is the largest owner of private radio stations in Ireland through his Communicorp group. Although he bought a new Gulfstream G650 jet last year, he exited aviation leasing group Aergo, where he owned an 80pc stake.

Other interests include the PGA Golf Tour courses and the Quinta Da Lago luxury resort in Portugal. There is a swathe of real estate ranging from a Marriott hotel in Haiti to what may become Dublin’s most expensive office block, the former Canada House on St Stephen’s Green.

He owns 75pc of China HR, which is rapidly becoming one of China’s largest recruitment firms. It sold its European operations for over €80m. He also owns the Topaz petrol station chain, which has revenues of €3bn per year, as well as the Siteserv Group, which is involved in infrastructure and facilities management, including the installation of water meters.

He moved into healthcare with the purchase of €100m worth of loans in the Beacon Hospital in Sandyford. But it’s not all work. O’Brien, regularly seen at Ireland rugby matches, is reported to have helped with the fee to bring Johnny Sexton back to Leinster and helps fund the salaries of our international football bosses Martin O’Neill and Roy Keane. O’Brien has bought a €90m luxury 1920s-style yacht called Nero, which had been built by Game boss Neil Taylor. O’Brien has also submitted plans to redevelop his Shrewsbury Road home into one of the country’s largest private residences, including an underground extension.

Heavily involved in the rebuilding of Haiti, he is also a philanthropist of note, widely known for his interest in corporate social responsibility.