Ronnie O’Sullivan’s outlook, opinions and mood often switch as quickly as the hand with which he plays a particular shot. He has descended from the highest of highs to the most miserable of lows and rebounded, all in the time it takes to progress from the first round to a trophy.

“I might be thinking and believing something today, but tomorrow I’ll probably change my mind,” O’Sullivan, bemused that the media hangs on his every word, once said. He is a self-perceptive individual who, even after three world titles and 42 professional tournament wins, is correct in describing himself as an underachiever.

No gathering illustrates O’Sullivan’s annoying yet enthralling unpredictability more vividly than the Maplin UK Championship, which begins at the International Centre in Telford today. Snooker’s most mercurial, unfathomable entertainer and enigma defends a crown that he has captured on four occasions, including in 1993 when, a week short of his 18th birthday, he became, and remains, the youngest winner of a world-ranking tournament.

He was the UK champion again in 1997, 2001 and last year, when, after compiling a break of 147 in the deciding frame of his 9-8 semi-final win over Mark Selby, O’Sullivan dismissed Stephen Maguire, at present his closest pursuer in the world rankings, 10-2 in a processional final.

Yet O’Sullivan has also plumbed the depths in the UK Championship, such as in 1994, when a quarter-final departure prompted the teenager to issue the first of countless threats to retire. Thankfully for a sport so in need of his panache, none has been carried out.

However, four years later, in the darkest period of a career then in peril from darker addictions, O’Sullivan withdrew from the event citing depression. In York in 2006, he stunningly shook hands in concession and walked out of the arena when trailing Stephen Hendry only 4-1 in a best-of-17-frames quarter-final.

O’Sullivan has confided that it was not the first, and almost certainly not the last, time he has been tempted to down tools in a fog of frustration but, ignoring the odd lapse, the world No 1 has shown more discipline and patience this year than before, en route to collecting prize-money of £504,750.

He sailed through the World Championship in April and May, added the Northern Ireland Trophy in August and last weekend, in Hopton-on-Sea, Norfolk, maintained his domination of the Premier League, an event that he has won for five consecutive years.

Anyone suggesting that this relative on-table serenity will continue indefinitely is either brave or foolhardy, but one overriding factor does appear to be a positive influence on his continuing level of determination: the release of his father, Ronnie Sr, who is serving a life sentence for murder, in 2010.

O’Sullivan Sr was jailed in September 1992. It was an incalculable blow to his adoring son, but their relationship has remained a deeply loving one throughout the incarceration and the prospect of the pair being together again at events, as they were week-in, week-out, during the player’s junior and amateur days, drives him.

“My dad says that watching me play on television is like a visit for him,” said O’Sullivan, who craves the day when Ronnie Sr can share in person a triumph at Wembley, the Crucible or wherever.

O’Sullivan’s father will no doubt be watching from his cell today when Ronnie Jr, a short-priced favourite for the UK Championship’s £100,000 first prize, plays Rory McLeod, a qualifier, in the last 32.

McLeod, the world No 44, is an interesting character. The only player of Afro-Caribbean descent on the tour, the 37-year-old Englishman is coach to the Qatar snooker team. However, success at O’Sullivan’s expense would represent one of the most unlikely results in the 31-year history of the championship.

The likes of Maguire, Selby and Neil Robertson, who won the Bahrain Championship last month, will be among those who fancy their chances but, at his best in two-session matches, O’Sullivan is tough to oppose. As always, his biggest danger is a 33-year-old from Chigwell, Essex - himself.

Four big names in danger of making an early exit

Graeme Dott The 2006 world champion arrives in Shropshire chronically low on confidence, having failed to survive his opening-round match in ten consecutive world-ranking events. His first opponent, Ken Doherty, has also struggled of late, but remains a wily campaigner.

Peter Ebdon His season began with an unexpected 5-0 whitewash by Liang Wenbo in the first round of the Northern Ireland Trophy and has not improved. He has won only one match in four world-ranking events and his place in the top 16 is under threat. Andrew Higginson could add to the woes of the 2002 world champion.

Mark Selby He could hardly have been given a more difficult initial test. The Masters champion plays Mark Williams, twice world and twice UK champion, who, having been relegated from the top 16 last season, is clearly a qualifier to be avoided.

Mark King The No 15 seed has the unenviable task of taming Judd Trump, the 19-year-old who beat Ronnie O’Sullivan on the way to his first world-ranking tournament semi-final at the Royal London Watches Grand Prix in October. Trump also earned an invitation to next month’s Masters by winning the qualifying event.

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