A sudden buzz crackled through the 2011 Oxegen Music Festival as one of pop’s starriest power couples — Beyoncé, who was performing on the final night, and Jay-Z — made their way backstage at the summer fete in the rolling countryside of County Kildare, Ireland. An older gentleman (bald, barrel-chested, in a black T-shirt) held open a door to the V.I.P. entrance for them. Sweeping past, Jay-Z pressed a $50 bill into the man’s hands, assuming he was a staff member or security — unaware he’d just tipped Ireland’s most beloved living musician, Christy Moore.

Moore closed the festival that night, as the surprise guest of the headliners, Coldplay. Performing his soaring 1984 anthem “Ride On,” he heard 60,000 fans roar at his introduction (“One of our heroes since we were kids,” Chris Martin announced), sing along at full volume and chant his name.

Born in nearby Newbridge, Moore had returned home after a long, celebrated career as a singer, songwriter, solo artist and leader of the groundbreaking folk band Planxty and the Celtic rock collective Moving Hearts. He’d become an icon, a national treasure — but a man still easily mistaken for the help.

“Once, at Carnegie Hall,” Moore recalled gleefully during a recent interview, “a critic wrote, ‘When Moore came out, I presumed he was a stagehand coming to move the piano.’ I think that review was OK.”

Moore, who turned 80 earlier this month, finds himself at a surprising professional peak. Last year, his 25th studio LP, “A Terrible Beauty,” debuted at No. 1 in Ireland, besting Sabrina Carpenter and Tyler, the Creator. Once a globe-trotting touring artist, these days Moore only plays his native island, performing solo — accompanying himself on guitar, bodhran drum or sometimes singing a cappella — while exploring a repertoire of songs that cut across 600 years of history.

Whether singing about the Blanket Protests (“90 Miles From Dublin”), detailing the Stardust nightclub tragedy (“They Never Came Home”) or pondering post-Troubles reconciliation (“North and South of the River,” his collaboration with U2), Moore has made a career charting his nation’s tragedies, triumphs and often difficult progress.