Garda Commissioner Martin Callinan today resigned after a 41-year career in the force.

He served in Dublin, Waterford and Mayo, and took charge of all the specialist units - drugs, fraud, immigration, and investigating organised and subversive crime.

A frontline policeman, he led the investigation into the Real IRA after the Omagh bombing, which resulted in Michael McKevitt being jailed for 20 years.

His tenure at the head of the gardaí has been difficult and controversial.

He was criticised for implementing the Government's policy of closing garda stations all over the country.

He never accepted the Smithwick Tribunal conclusion that the gardaí placed loyalty to the force over honesty.

He was also involved in a long-running row with the Garda Ombudsman Commission.

Commissioner Callinan also found it very difficult to listen to allegations of widespread corruption in the force made in the Dáil, by garda whistleblowers and elsewhere. Those allegations are now the subject of a number of inquiries.

The seeds for today's announcement were sown in January when he appeared before the Public Accounts Committee and described as "disgusting" the actions of the garda whistleblowers in downloading and disseminating personal and sensitive data from the garda's PULSE computer system.

The comment placed him at the centre of a political controversy.

However, the pressure on him had been easing until last Thursday when Minister for Transport Leo Varadkar reignited the penalty points controversy.

The Fine Gael minister's comment was rapidly followed by similar statements from Labour and opposition politicians and today Mr Callinan announced his resignation.

This morning the commissioner announced he was resigning for family reasons.

Deputy Commissioner Noirín O'Sullivan now takes temporary charge of a force, which is supposed to be apolitical but has been directly affected by the words and deeds of politicians.