Ian Paisley, a Protestant who set aside decades of hatred to share power with his Catholic foes, will step down as Northern Ireland's First Minister in May.

A spokesman for the 81-year-old Protestant cleric who has been a towering figure in Northern Irish politics for half a century said he would step down after hosting a visit by top U.S. business executives that ends on May 9.

Northern Ireland's rival politicians are hoping to attract foreign investment to the province, ravaged by three decades of bloodshed that ended with a peace deal in 1998 and a historic power-sharing agreement last year.

Irish Prime Minister Bertie Ahern described Paisley as a "giant figure in the history of these islands" and expressed confidence that peace was secure in Northern Ireland.

"I can say with certainty that the leadership he has shown in recent years means that future generations of Irish people, North and South, will live in a peace and prosperity that previous generations could only dream of," Ahern said.

The Good Friday Agreement reached in 1998 largely ended 30 years of violence in Northern Ireland that killed more than 3,600 people, but tension persists in some parts of the province between the Protestant majority and the minority Catholics.

Martin McGuinness, the province's deputy first minister and a senior member of the predominantly Catholic Sinn Fein party, described Paisley's departure as the end of an era.

"It's obviously a momentous decision for him and for the political process, but obviously I look forward to working with whoever is elected leader of the DUP and first minister," said McGuinness, a former commander in the Irish Republican Army.

HUGE CONTRIBUTION

McGuinness told Irish radio last year's deal between Irish nationalist Sinn Fein and Paisley's pro-British Democratic Unionist Party had been "one of the most historic political breakthroughs in the history of the island of Ireland."

He and Paisley have been dubbed the "chuckle brothers" after a string of unexpectedly jovial and friendly joint appearances over the last year that are seen as one of the most potent indications of how much things have changed.

Paisley himself was once best known as a burly, bull-necked preacher with the loudest voice in Northern Ireland who would bellow "No Surrender to Dublin" from pulpit and husting.

Sinn Fein President Gerry Adams said there was no reason anybody should be concerned by Paisley's departure.

"He (Paisley) had a certain personality and whoever is the new leader will bring their own personality and characteristics to bear," Adams told Reuters.

Paisley's son, Ian Paisley Jr, resigned as a junior minister in the Northern Ireland power-sharing government last month, bowing to criticism of his links to a property developer.

Paisley said he was not stepping down because of his son's tribulations. "That had no effect on me whatsoever ... In fact, it hardened me to realise there was no easy path and we had to prepare for the rough and the smooth," he told BBC television.

Prime Minister Gordon brown said Paisley had made a "huge contribution" to political life in Northern Ireland.

"The whole country values and admires the manner in which he has led as First Minister," Brown said.

Paisley's deputy Peter Robinson is odds-on favourite with bookmakers to take over as head of the DUP but Paisley refused to be drawn over his successor.

"The DUP is not the Roman Catholic church. We don't have apostolic devolution. It comes by the votes of the people."