Mr Ahern has been taoiseach since 1997
Taoiseach Bertie Ahern will go down in history as a key figure in bringing peace to Ireland.
But his decision to leave office is unlikely to keep him out of the news, with difficult times ahead at a judicial tribunal investigating corruption. Diarmaid Fleming reports from Dublin.
"Now I'll submit to the verdict of history," said Bertie Ahern, closing his speech to the Irish Parliament, on the day he announced he is to leave the highest political office in Ireland which he has held since 1997, after three consecutive general election victories.
As the applause of his parliamentary colleagues rang out in the chamber, he may have been a little premature: it is unlikely that the last pages of history involving Ahern are ready for drafting.
But Bertie Ahern has already earned his place in history as the leader of the Republic of Ireland who played a key role in bringing lasting peace to the island.
His political pedigree as a conciliator and negotiator - stemming from his early political career as an industrial-relations trouble-shooter and dispute deal-clincher - helped him forge the historic political settlement leading to power-sharing in Northern Ireland last year.
Ahern's ability to bring political opposites together, and build trust among those at both ends of the Ulster political spectrum - from Ian Paisley of the Democratic Unionist Party to Sinn Féin's Gerry Adams and the IRA was probably the crucial ingredient which led to the cementing of a lasting political deal.
His unique relationship with former British Prime Minister Tony Blair, who came to power at the same time as Ahern in 1997, and their tenacity in sticking with ten years of negotiations rocked by difficulties, drove the process.
But Ahern brought the common touch, charisma and charm, and an ability to deal with people from all backgrounds on their own level, a hallmark of his career and political popularity over decades.
Mr Ahern featured in Jonathan Powell's memoirs
In his recently published memoirs, Blair's former long-time chief-of-staff Jonathan Powell said that while Blair would be in his room after talks, Ahern would be working the bars and tables to inch forward the negotiations, or mend the divides between the sides.
Ahern's supporters and opponents alike say he was the key to solving what was insoluble to every previous leader of the Irish state: a conflict which nationalists say has afflicted Ireland and Britain over 800 years.
Politicans on both sides of the Irish Sea and the Atlantic heaped praise on Ahern's role, after his shock announcement that he intends to step down.
Despite his historic place in resolving the Northern Ireland conflict, storm clouds loom in the sunset of his career, emanating from the Mahon Tribunal investigating corruption in the planning process in the Republic.
In a strange irony, a judicial forum set up by Ahern's first government in 1997 may prove his nemesis.
Dublin has been the scene of a huge property boom over the past decade, but also haphazard planning, in part fuelled by corrupt land deals rubberstamped by some local council politicians affiliated to the three main political parties, Ahern's Fianna Fáil, Fine Gael and Labour.
Re-zoning of land from agricultural to building land made multi-millionaires from the landowners, developers and builders who profited.
Newspaper reports by investigative reporter Frank Connolly linked senior politicians in Ahern's party to corruption.
Close political associate and foreign affairs minister in Ahern's first government, Ray Burke, resigned over the allegations in 1997, and was later convicted and jailed for corruption.
The Mahon Tribunal was established to examine allegations of corruption, and has become Ireland's longest-running judicial inquiry.
Ian Paisley presents Bertie Ahern with a ceremonial gun
An allegation by English-based Irish developer Tom Gilmartin that Bertie Ahern had received £80,000 from a rival developer Owen O'Callaghan sparked the investigations by the tribunal into Ahern's affairs.
Both Ahern and O'Callaghan deny such payments were made, but tribunal lawyers discovered over £100,000 of unexplained payments into accounts linked to Ahern.
News that Ahern was being investigated by the tribunal came in newspaper reports in September 2006, with Colm Keena of the Irish Times revealing he had received between 50,000 and 100,000 euros from businessmen.
Ahern reacted furiously to reporters' questions and said he had acted properly at all times, adding that the figures quoted were "off the wall".
"What I got personally in my life is, to be frank with you, is none of your business," he said.
"If I got something from somebody as a present, if I got money from a family member or something, but I have given that detail to show I got nothing wrongly and I dealt with properly in my books."
But Ahern's private finances soon became very public news.
Shortly after the reports, he gave a showcase interview to national broadcaster RTE, in which he stated he had received financial help from friends and businessmen, some of who he had appointed to state boards.
Three in a row
He survived a vote in parliament, and won a third election victory in a row despite the allegations that he had received unexplained payments.
But his political difficulties began in earnest when he gave evidence at the tribunal last September, December and February.
Revelations at the tribunal have found unorthodox financial arrangements, cited by Ahern himself when he revealed he did not operate a bank account while he was minister for finance in the early 1990s.
He said this was his personal choice, just as it was for people to adopt unusual fashsion. Ahern explained his staff cashed his cheques, and left money in bundles of up to IR£1500 on his desk if he was not around.
The tribunal heard Ahern explain he received around £8,000 sterling from businessmen in an impromptu whip-around after a speech in Manchester while finance minister, and two so-called 'dig-outs' for IR£22,500 and IR£16,500 in 1994 and 1995.
He says these were to help him through a difficult marital separation with his wife, and to buy a house.
While overseas donations were tax-free in Ireland in the mid-1990s meaning there was no tax liability on the £8,000, Ahern's other financial 'dig-out' donors have given evidence under oath to the tribunal backing his claim that the 'dig-outs' were loans therefore not requiring him to pay tax.
The cash was not declared to the Irish tax authorities, the Revenue Commissioners.
But the tribunal found no paperwork relating to the loans, and also discovered that Ahern had not made any repayments for over 11 years until he paid them back in full to his donors in 2006, with many forwarding this money to Ahern's ex-wife's charity.
Mr Ahern won three elections in a row
Other evidence emerged of large sums of money, including his former landlord Michael Wall arriving from Manchester with a briefcase of over £27,000, which Ahern says was to pay for refurbishments to the relatively new rented house.
The tribunal's investigators have found that over two-and-a-half times Ahern's salary was lodged into accounts on his behalf in 1993 and 1994.
They also claim that two sums lodged on his behalf equate exactly to £25,000 sterling and $45,000.
The tribunal also found that Ahern had savings of more than £50,000 during the time he took what he says was the unsolicited dig-out loans.
Mr Ahern has denied dealing in foreign exchange apart from the £8,000 Manchester money.
Locking of horns
But Tribunal lawyer Des O'Neill SC who has locked horns with Ahern in sometimes angry exchanges at hearings has challenged the Taoiseach's accounts of his finances.
The tribunal is probing if the money received by Ahern came to him as he says, or whether the stories of dig-outs and whip-arounds are bogus, and if he received the money from other routes or donors.
They are also probing if Ahern was seeking to hide money from his wife during his marital separation proceedings. Ahern denies all such allegations.But recent evidence led to new difficulties for Ahern.
The tribunal heard in February that IR£30,000 of Fianna Fáil party funds were loaned by his local party Ahern's then girlfriend, Celia Larkin, to buy a house for IR£40,000 in which her aunts lived in the 1990s.
The Mahon Tribunal took place in Dublin
She now owns the house worth over £800,000.
And evidence given by a former building society at the tribunal just before Easter provided conclusive proof that Ahern had £15,500 sterling lodged into his own and his daughters accounts by his local party office secretary Gráinne Carruth.
After warnings of the consequences of perjury, she admitted that she had probably made the lodgements.
The presence of large amounts of sterling lodged on his behalf contradicts all of Ahern's previous statements to the media and tribunal evidence, and sparked a growing political crisis.
He is yet to give his explanation, expected at the tribunal when he returns to give evidence at the end of May.
Ahern denied his announcement to step down was linked to this recent evidence at the tribunal, but this is difficult to believe.
While he will soon be untroubled by the affairs of the highest political office in Ireland, Ahern is unlikely to be enjoying quiet retirement with the mounting difficulties he appears to face at the tribunal.
The inquiry is examining financial transactions linked to him totalling IR£452,800 according to the Irish Times.
His unorthodox financial arrangements are also under investigation by the Revenue Commissioners probing tax evasion which Ahern denies.
Contradictions in his evidence raised by the recent £15,500 revelations also will place his previous testimony at the sworn inquiry under scrutiny.
Ahern has complained that the tribunal is unfair, a further irony given that the judicial body and its rules were set up by his first government.
Its judgment is not expected until at least next year. Ahern will hope history will judge him for his role on other matters, but the tribunal could bring difficult footnotes to the historical biography of Ireland's most prolific and enigmatic politician of the present generation.