Nearly all of the presidents of Ireland have been affiliated to a political party. Most have retired from active politics. Mary McAleese was a notable exception (law professor fro NI) but her candidacy was still nominated by Fianna Fail and the Progressive Democrats as well as herself.
Presidents of Ireland list:
en.wikipedia.org/wiki/President_of_Ireland#List_of_presidents_of_Ireland
Most of the presidents have been affiliated with the Fianna Fail party and have had long political careers. Erskine Childers was the son of a notable participant in the 1916 Rising on top of his own political career. Eamon deValera dominated Irish politics from the 1916 Rising on.
Of late, presidents have been affiliated with the Irish Labour party too - Michael D. Higgins had a long, long career in politics before becoming president, football and rugby fan in chief, First ATM User, and all around national treasure.
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The office of president is supposed to be politically neutral. The president is advised by the Council of State.
en.wikipedia.org/wiki/Council_of_State_(Ireland) members and role here, along with history of presidential constitutional role and activity.
While some individuals have run for president in the recent past without any political experience and without a professional background in law or administration, Irish voters tend to view these two elements of a candidate's background as essential for fulfilling the role.
The president has discretionary powers and reserve powers. The only power that is solely the president's is to refuse to grant a dissolution of the Dail if a Taoiseach as lost a vote of no confidence.