What to Know About Jeffrey Donaldson, the Former D.U.P. Leader in Northern Ireland

Jeffrey Donaldson, who resigned as leader of Northern Ireland’s Democratic Unionist Party on Friday, has spent his career defending the political union between Britain and the six-county statelet where he was born 61 years ago.

Northern Ireland’s longest-serving member of Parliament, he has been present at most of the pivotal moments in its recent political history. His sudden resignation, after being charged with non-recent sexual offenses on Thursday, has upended the status quo in Northern Ireland and raised questions about the future direction of the Democratic Unionist Party, or D.U.P.

Michelle O’Neill, the first minister of Northern Ireland, said on Friday that the charges against Mr. Donaldson were “now a matter for the criminal justice system” and added that her priority was to “provide the leadership the public expect and deserve, and to ensure the four-party executive coalition delivers for the whole of our community now and in the future.”

Here’s what to know about Mr. Donaldson’s career and his impact on politics in the region.

His route to power.

Born in Kilkeel, a County Down fishing and farming village that is within sight — across a narrow sea inlet — of the independent Republic of Ireland, Mr. Donaldson was the eldest of five boys and three girls.

In 1970, during the period of sectarian violence between Protestant unionists and Catholic nationalists known as the Troubles, his cousin Samuel Donaldson was killed by the Provisional Irish Republican Army while serving in the Royal Ulster Constabulary, an event that Mr. Donaldson would later say “shattered” his childhood.

He joined the Orange Order, a Protestants-only religious and cultural group, at age 16, and two years later enlisted in the Ulster Defense Regiment, a heavily Protestant part-time militia unit of the British Army that was deeply engaged in the Troubles.