When NYPD Det. Joseph Lemm moved to New York City years ago, friends called him “Country Boy” — a suitable nickname considering his roots in Beemer, Nebraska, population 800.

Lemm’s fellow officers in the NYPD fashioned him with another moniker — “Christopher Reeve” — because his rock-solid 250-pound, 6-foot-5 frame and movie star looks gave him more than a passing resemblance to the late actor famous for playing Superman.

Tuesday, as Lemm’s family, friends and co-workers in the NYPD mourned his death after a suicide bomber on a motorcycle attacked his unit in Afghanistan, they also remembered his life and the mission he carved into it: a dedication to his country, no matter the cost.

VideoSoldier makes surprise visit home in 2013

“He wanted to protect and serve,” said his mother, Shirley Lemm, in a phone interview before she traveled from Beemer to Dover Air Force Base in Delaware to await the return of the body of her son, 45.

“He loved people and loved life.”

The 15-year NYPD veteran was serving in the Air National Guard when the attacker — his motorcycle loaded down with explosives — slammed into Lemm’s unit, killing him and five other American service members, including his overseas roommate, Air National Guard Staff Sgt. Louis Michael Bonacasa, 31, of Coram.

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Funeral arrangements have yet to be made for Lemm, married with a young son and stepdaughter, said a family friend in Westchester County where he lived. Lemm also had a brother, Brian, the friend said.

Coming a year and a day after the shooting deaths of detectives Rafael Ramos and Wenjian Liu, Lemm’s death hit the NYPD hard. He is the third NYPD cop killed in Mideast conflicts since the U.S. invaded Iraq in 2003.

Det. Deon Taylor, a SUNY Old Westbury graduate serving with the Army National Guard, was killed in 2008 when a bomb exploded under his vehicle in Bela Beluk, Afghanistan. In 2005, a sniper shot and killed Det. James McNaughton, 27, in Iraq. McNaughton, a graduate of Centereach High School, was a staff sergeant with the Army Reserve’s 306th Military Police Battalion in Uniondale.

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Lemm’s boss in the NYPD’s Bronx warrant unit described him as a brave cop with hundreds of arrests to his credit.

“He was fearless,” said Capt. William Kivlehan, “had a great demeanor.”

As tough as he was, Lemm had a soft heart.

Kivlehan said when the work demanded a predawn raid, Lemm would be in the office an hour early with fuel for the sleep-deprived unit — coffee and bagels.

“He was that kind of guy who cared about everybody else,” Kivlehan said.

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Lemm’s partner in the warrant squad, Det. John McCrossen, said the detective liked to take his boat on Long Island Sound to watch Fourth of July fireworks, accompanied by family and friends.

Shirley Lemm said her son first signed up for a four-year hitch in the Air Force in 1989. After his discharge, she said her son bounced from job to job. He moved east and joined the NYPD in 2000.

Back home in Beemer, Shirley Lemm said the locals wanted her to know they’ll never forget her fallen son.

“We may be a small town but we have a big heart,” she said they told her after news of his death spread across the tiny prairie town in Nebraska’s northeast corner.