Niall Stanage is a staff writer for The Hill newspaper in Washington.

Rory McIlroy’s religion was, until a few days ago, a mystery to Barry McGuigan.

“Is he Catholic? Really?” McGuigan said. “I didn’t know that. I thought he was a Protestant young guy.”

McGuigan was a precursor of a kind to McIlroy, the young golfer who has become Northern Ireland’s latest sporting hero in the wake of his United States Open triumph last month.

But the differences in the stories of the two men are as illuminating as the similarities, especially when it comes to the changing nature of their homeland.

McGuigan, a charismatic boxer, rose to become a world featherweight champion in the mid-1980s. A Roman Catholic born and raised in a small town just over the border in the Republic of Ireland, he threaded his way through the political and cultural minefield of the time to become beloved by almost everyone.

Back then, the three-decade violent struggle that tore Northern Ireland apart — known euphemistically as the Troubles — had settled into a dismal pattern.

Pro-British paramilitary groups, who labeled themselves loyalists, and their Irish republican opponents, most notably the Irish Republican Army, engaged in killings that were as savage as they were futile. Bodies were found in city back alleys and on damp country roads with numbing regularity. The gloom was all-encompassing and, it seemed at the time, endless.

McGuigan’s broad popularity was a sizable achievement, pulled off only through repeated and ostentatious displays of neutrality. He refused to have national flags accompany his entrance into the ring. In place of a national anthem, he would have his father sing “Danny Boy” before his bouts. Even his shorts were adorned with a dove of peace.

McIlroy enjoys a similar cross-community appeal. But, tellingly, he has acquired it without advertising his impartiality in blazing neon. He has, so far, dodged questions of political affiliation with a shoulder-shrugging casualness that no one from McGuigan’s era could have gotten away with....