HAMPTON, N.H. — The little boy was a water bug. A preternaturally strong swimmer, he didn’t linger by the seashore, digging moats around crooked sand castles with the other little kids.

He was in the ocean. He was befriending lifeguards 10 years older than he was. It’s where he felt he belonged.

He became their mascot of sorts. Tall and strong and bronzed, those lifeguards liked the little kid and happily took him under their well-toned wings.

He learned their names and their schedules, and he admired their minimalist uniforms: fluorescent orange swimsuits that announced they were part of the Hampton Beach rescue squad. So even at age 7, little Jimmy Donahue knew what he wanted to be when he grew up.

“I thought it was the greatest job in the world from the get-go,’’ Donahue said the other morning in his office overlooking a pristine, sun-dappled coastline at the beginning of his 58th summer on guard at Hampton Beach.

Yes, that kid who became a lifeguard at age 16 is 73 years old now. He’s still at his post. Still at the edge of the Atlantic Ocean, watching for riptides, and lost children, and any signs of trouble in the pounding surf.

“You love helping people,’’ he said. “The kids keep you young. It’s been fun. It really has. There’s no better feeling than to realize at the end of the day when you’ve been involved in a rescue that perhaps you just saved a human life.’’

Donahue has rescued hundreds of them – upward of 500. His is a remarkable career that stretches back to 1960 and the twilight of the Eisenhower presidency. Like a reliable lighthouse beacon, he’s always been there.

Through JFK’s Camelot and warfare in the jungles of Vietnam. Through the Reagan revolution and the malaise of Jimmy Carter. The Berlin Wall toppled, and Bill Clinton built his bridge to the 21st century. Transistor radios morphed into boomboxes and then iPods. Through it all, there was always Jim Donahue and Hampton Beach.

Swimsuit fashions changed. The Rolling Stones gave way to Nirvana. The Red Sox, long a dependable cellar dweller, won a world championship. Then another. And another. And against that backdrop, Donahue was a dependable seashore metronome. Always there. Always on guard.

“Holy mackerel, nobody could be a better ambassador for the state of New Hampshire, I can tell you that,’’ said B.J. “Doc’’ Noel, president of the Hampton Area Chamber of Commerce. “If anything happens to anyone, he takes it very personally. He’s a very caring guy. And no one knows Hampton Beach better than him.’’

A 1962 graduate of Malden Catholic High School, he was raised in Woburn and first arrived here at age 3. His grandfather, a former Cambridge fire chief, had a nearby cottage that became Donahue’s home from late June to Labor Day.

He remembers the old carnival, where human cannonballs once sailed over the top of the bandstand near the lifeguard station that now bears his name.

He peddled newspapers, redeemed bottles at 2 cents a pop, and washed dishes at the Hampton Beach Casino until he turned 16 and one of those lifeguards he once shadowed told him: “You’re one of our guards now.’’

The job stuck. And it’s the chief reason he earned his bachelor’s degree in science and physical education from Boston University in 1967. That was his ticket to a career in teaching, a job that enabled him to return to Hampton Beach each summer.

To say the sandy shore here has become part of his DNA is hardly hyperbole.

It’s where he met Joanie Murphy, the little girl who admired him in his swimsuit when she was just 12. They reconnected years later at a seaside cafe. He asked for a dance and, later, her hand in marriage. They married in 1974.

“I was a cradle robber,’’ he said. “She’s eight years younger than me.’’

It’s where he drew the ire of then-New Hampshire Governor Meldrim Thomson Jr., who in 1976 upbraided Donahue for closing the beach after he sighted a 12-foot shark just 30 yards from shore.

“He criticized me openly,’’ Donahue recalled. “The governor said, ‘Who the hell is Jim Donahue to shut down Hampton Beach? Only I can shut down Hampton Beach.’ I personally saw sharks myself, so I had to shut down the beach.’’

It’s where he watched schools of bluefish nibble on the feet of terrified bathers. It’s where he compressed the rib cages of countless overwhelmed swimmers, firmly and steadily coaxing them back to life.

He once stood on the beach with his brother Kevin, then also a lifeguard, when he noticed a strong storm building from the south and a small plane caught in its furious winds.

“The wing actually clipped the sand maybe 30 yards in front of me,’’ he said. “Just then, a wall of water and wind picked it up like it was a toy and flipped it over into the water. My heart was pounding. I thought I was going to die. I thought I was doing to die from an exploding plane, from lightning on this wet fuselage. I jumped up and opened the door and the poor guy. The water was already discolored from his blood.’’

The pilot was dead before they could get him out of the plane.

Mementos of his time on Hampton Beach adorn the walls of his new office overlooking the umbrella-dotted sand. A letter of admonishment that his supervisor sent to Governor Thomson is there, calling Donahue a “credit to himself and to the state.’’

There are rows of photos of the assembled rescue teams he guided and shaped, including some with his two sons, who followed him onto the beach, first with tailored orange swimsuits their mother crafted to fit their boyish bodies, and later as full-fledged lifeguards.

“You got a sense from the other lifeguards of how much they admired my father and how they looked up to him and how, at different points in their life, he helped shape where they were going,’’ said Kevin Donahue, now 33 and the director of operations for an organic products company in Portsmouth. “He’s such a part of the beach, and the beach is such a part of him.’’

Julie Leonardmanages the beach office for the local chamber of commerce, but traces her friendship with Donahue back 50 years when, just after college, Jim Donahue was a part-time bartender at the Ashworth by the Sea Hotel, where she worked as a cocktail waitress.

“Jimmy was the best thing that ever happened to Hampton Beach,’’ said Leonard, a retired Chicopee school principal. “He’s wonderful to his lifeguards. He demands a lot but he gets a lot. He is Hampton Beach, when you think about it.’’

Leland Brennan has thought about it. And agrees. Brennan is a former dean of students at Whittier Regional Vocational Technical High School in Haverhill, where Donahue worked as a physical education teacher until his retirement in 2003.

“Jimmy’s the type of guy where if you need a pat on the back, he’ll give you a pat on the back,’’ said Brennan, now Donahue’s right-hand man at the beach. “If you need to be spoken to, he’ll be the guy who will speak to you. He’s quite a guy.’’

Yes. A guy whose summer routine kicks into high gear this week, when he and that girl he once met on the beach will celebrate their 43rd wedding anniversary.

“I’ve never been anywhere else in the summertime than Hampton Beach,’’ he said.

And then he told me something else: Maybe it’s time to leave his job as chief of the Hampton Beach Patrol Surf Rescue.

“Oh, 58 seasons of doing this, it’s hard to say goodbye,’’ he said. “I keep saying to one of my captains, ‘This is it.’ It could be this year. If I ever did, I would ask that I could come back in some role and be part of this organization.’’

Part of this organization? In some ways, Jim Donahue is the organization, as familiar and reliable as the relentless ocean’s furious surf he’s patrolled nearly all of his life.

Thomas Farragher is a Globe columnist. He can be reached at thomas.farragher@globe.com.