For two decades Silvio Berlusconi seemed Teflon-coated, untouched by dozens of court cases and scandals, dominating political life and becoming Italy's prime minister four times.

But on Thursday, judges finally caught up with the flamboyant 76-year-old when the Supreme Court rejected his appeal against a four-year jail sentence — commuted to one year under a general amnesty for crimes committed before 2006 that the government instituted in an effort to ease prison crowding.

It ordered a review of the second part of the sentence — a five-year ban from public office for tax fraud — but the ruling was nonetheless a devastating blow that could at last signal the political twilight of Italy's greatest showman.

The billionaire media mogul, Italy's most colourful and scandal-prone figure but also its most skilful politician, has never previously been finally convicted in up to 30 court cases launched against him.

He is unlikely to actually serve time in jail as felons in Italy who are over the age of 70 generally serve out their sentence doing community service or under house arrest. It is also unusual for first-time offenders with a sentence as short as one year to serve jail time.

In a video-address released after the decision was revealed, Berlusconi said the sentence was baseless and that it deprived him of his freedom and political rights.

The longtime politician and business mogul said he is the victim of "an incredible series of accusations and trials that had nothing to do with reality."

Berlusconi denied the fraud claims and said that he has been harassed by a biased judicial system for years.

Looking shaken, he vowed to press ahead in politics with the refounding of his original political party, Forza Italia, through the mobilization of young people, and a reform of the justice system. But he acknowledged that he had "arrived almost at the end of my working life."

Self-made man

Even though the ban on holding public office is under review, Berlusconi's ability to exploit his campaigning and communication skills will be severely limited.

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Berlusconi was convicted of having sex with Moroccan-born nightclub dancer Karima El Mahroug when she was under age, but he has two chances to appeal the conviction, meaning the case could drag on for years before it is resolved. (Stringer/Reuters)

He says he has been systematically persecuted by leftist magistrates bent on perverting democracy since he stormed into politics as a new force in 1994 after a massive bribery scandal swept away the postwar political order.

One of Italy's richest men, whose self-made image is a big part of his appeal, Berlusconi has a business empire that includes construction, media and the AC Milan soccer club. He has made a career of confounding pundits who repeatedly counted him out.

But this time, his chances of bouncing back look slight, despite his supporters' insistence that he will continue to lead his centre-right People of Freedom (PDL) party.

No apparent successor on horizon

Berlusconi has failed to groom any strong successor, and there is speculation his oldest daughter, Marina, 46, who is the chairwoman of his Fininvest holding company, will become the PDL figurehead.

The ruling has huge implications that go way beyond the impact on Berlusconi himself, and could seriously endanger Italy's uneasy left-right coalition government.

Widely known as il Cavaliere, or the Knight, because of a state decoration, Berlusconi looked down and out for much of 2012 after a jeering crowd hounded him from office in November 2011 as Italy came close to a Greek-style debt crisis.

Months of indecision over whether to stand in an election brought his PDL to the brink of disintegration in late 2012, with the party garnering less than 15 per cent of public support in opinion polls. Pundits widely predicted that he was finished.

But Berlusconi was suddenly energized after precipitating the fall of his successor, technocrat Mario Monti, in December last year. Diving into the campaign, he once again showed unrivalled mastery of communication and ran rings round his lacklustre rivals on the left and centre.

He came within a whisker of success, losing to the centre-left Democratic Party (PD) by less than one per cent.

Underage sex conviction not final

Berlusconi joined a coalition with centre-left Prime Minister Enrico Letta and appeared to be thriving, with the PDL topping opinion polls — until his legal troubles caught up with him.

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Anti-Berlusconi protesters gathered outside Italy’s highest court building. (Riccardo De Luca/Associated Press)

In June, he was sentenced to seven years in jail for abusing his office and paying for sex with the Moroccan-born nightclub dancer Karima El Mahroug, alias "Ruby the Heartstealer" when she was under age.

The case splashed allegations of lurid "bunga bunga" orgies at Berlusconi's villas across the newspapers, finally alienating some of his most loyal conservative supporters.

But the mogul has two appeals before that conviction becomes effective. Thursday's case is much more serious now that the verdict is final.

Signature off-colour humour

Berlusconi is one of the most extraordinary characters to come out of Italy's often bizarre political landscape, possessing a unique mix of political talent, brazen behaviour and a propensity for diplomatic gaffes that led to his virtual ostracism from European summits before his fall in 2011.

But in government, he consistently showed himself to be better at promises than action, failing to implement pledges to liberalize an inflexible and uncompetitive economy despite his landslide third election victory in 2008.

Italy's longest-serving prime minister is known for irrepressible off-colour humour, his facelifts, perennial tan, make-up and hair weave.

But his flamboyant personality hides a keen political mind and an almost uncanny talent for tapping into the fears and concerns of ordinary Italians.

His success in clawing back a 10-point centre-left lead before February's election was largely down to populist tactics such as homing in on a painful housing tax imposed by Monti and attacking German hegemony in Europe.

His energy was remarkable for a man of his age, with most of his mainstream opponents unable to compete with a storm of television appearances where he rarely lost his cool and showed off his talent for off-the-cuff quips that some Italians would laugh about for days afterward.

His wife, Veronica, left him in 2009, accusing him of consorting with underage women. He was last year ordered to pay her a settlement of 100,000 euros ($136,637) a day. But he even made campaign jokes about that.

On Thursday, his legendary luck finally ran out.

With files from CBC News and The Associated Press