Frank Sinatra Jr. and his father in 1963. (AP)

Frank Sinatra Jr., who was blessed and cursed to be the echo of his father’s voice, who survived a kidnapping as a teenager, later conducted his father’s orchestra and, as a singer, re-created the Sinatra sound with uncanny ­fidelity, died March 16 in Daytona Beach, Fla. He was 72.

The cause was cardiac arrest, his family said in a statement. Mr. Sinatra was on tour, singing his father’s classic music from the great American songbook.

Mr. Sinatra became a public figure at his birth, during his father’s first blaze of fame as a singing idol. Although he was not technically a “junior,” he was his father’s only son and became known by the diminutive, second-generation term. He struggled throughout his life to build an identity of his own.

He had a contentious relationship with the elder Sinatra, who was often called the greatest singer of popular music of the 20th century but was absent for much of his son’s childhood.

From time to time during his performances, Frank Sinatra Jr. would say, “I am now going to devote five minutes to the music of Frank Sinatra because that is exactly how long Frank Sinatra devoted to me.”

Frank Sinatra Jr. in 2008. (Caio Leal/AFP/Getty Images)

His parents divorced when he was a child, and Mr. Sinatra grew up in his mother’s home in Los Angeles with his two sisters, Nancy and Tina. Still, he was never far from his father’s orbit and often attended his recording sessions and nightclub performances. He learned all of his father’s music by heart and, from an early age, sang at family gatherings.

He became a proficient musician and enrolled at the University of Southern California with ambitions of being a pianist and composer. He joined a singing group at Disneyland, then left college to become a vocalist with the Tommy Dorsey orchestra, one of the bands that helped launch his father’s career. (Dorsey died in 1956, but his “ghost band” continues to perform under his name.)

“He knows — and projects — the inflections, the shading, the phrasing that his father used,” New York Times music critic John S. Wilson wrote in 1963. But a less charitable critic for Newsweek described his singing as “mimicry.”

Even though he was billed as Frank Sinatra Jr., he never had the natural charisma on stage that his father had. There was a family resemblance, but his eyes were brown, not blue.

In December 1963, when he was 19, Mr. Sinatra was abducted at gunpoint from a Lake Tahoe hotel. He instantly became the country’s most famous kidnap victim since the Lindbergh baby in 1932.

During a bizarre cat-and-mouse game, the kidnappers negotiated with the elder Sinatra through a series of phone calls to out-of-the-way gas stations. They demanded a ransom of $240,000 — even though the entertainer willingly offered $1 million.

As the four-day ordeal unfolded, Mr. Sinatra was held hostage and driven around California in the trunk of a Chevy with a bad muffler. After the ransom money was delivered, the kidnappers released Mr. Sinatra, who was walking to his mother’s house when he was found by a police officer.

When he saw his father, the first thing he said was, “I’m sorry, Dad.”

After three men were arrested and put on trial, one of their lawyers suggested that Frank Sinatra Jr. had coordinated the abduction as a publicity stunt. Even after the kidnappers were sent to prison, the false accusation created a lingering sense of suspicion about Mr. Sinatra.

During the 1960s, his father’s career continued to flourish with hit records and movie roles, and his sister Nancy found success as a pop singer. But Frank Sinatra Jr. was destined to become a nostalgia act before he turned 25.

“Over all these years,” he told Britain’s Telegraph newspaper in 2012, “I have never had a hit movie, never had a hit television program and never had a hit record. To my way of thinking, that means success has not been achieved. I have made no mark of my own creation.”

Franklin Wayne Emanuel Sinatra was born Jan. 10, 1944, in Jersey City. He was the second of three children from his father’s first marriage, to the former Nancy Barbato.

For years, Mr. Sinatra found modest success singing in lounges and nightclubs and took occasional acting jobs in films and television. In later years, he played himself as a member of a group of poker players on “The Sopranos,” and he did voice-overs of himself in the animated series “Family Guy.”

He was married in 1998 to Cynthia McMurrey, a Texas lawyer. They divorced two years later. He had a son, who teaches in Japan, from a previous relationship. Other survivors include his mother and sisters.

In 1988, Mr. Sinatra received a call from his father asking him to become his musical director. For seven years, he helped burnish the elder Sinatra’s legend in concerts all over the world. He kept his back to the audience, wearing a tuxedo with a dull finish because he didn’t want to outshine his father.

If the band made a mistake in rehearsal, the singer often berated his son, who took the abuse as part of his musical and filial duty. If his father forgot the lyrics to a song, his son would sing them while conducting, as if to guide his father back on course.

Mr. Sinatra described himself as his father’s “aide-de-camp.”

“I have to see that my general is prepared at all times,” he told GQ magazine in 1994, “that he never goes into battle unprepared.”

Frank Sinatra gave his final performance in 1995 and died three years later at 82.

His son kept the flame alive until the end, traveling all over the world with a show called “Sinatra Sings Sinatra.”

Even after his father’s death, Mr. Sinatra maintained a sense of formality and distance toward him. He rarely spoke of him as “Dad” or “my father,” but would call him “Frank Sinatra,” as if talking about a stranger.

“My lack of success does not trouble me at this stage in my life, no,” he said in 2012. “When I was younger, sure, I wanted to have some degree of, shall we say, identity. But it never came.”