David Cassidy, the actor, singer and teen heartthrob with the green eyes and the feathered haircut was the magical success of “The Partridge Family,” the 1970s television show about a family band. The band’s songs, sung by himself and his stepmother, Shirley Jones, were all the rage in the early seventies. It had several notable starts, Danny Bonaduce and Susan Dey amongst them. Shirley was already a big musical name coming from Rogers and Hammerstein’s 1950s musicals.

David played Keith Partridge, the eldest of five children in a family that forms a band and goes on tour in a multicolored bus. Mr. Cassidy had a face youthful enough to portray a teenager, a shy smile and friendly eyes, and he had a wonderful voice. The show called “The Partridge Family” lasted from 1970 to 1974 and made David a teenage idol.

In 1972, in what he recalled as a career peak, Mr. Cassidy headlined Madison Square Garden, wearing the white jumpsuit ala Elvis Presley, but by then he was already weary of incessant career demands and squealing mobs. To spice up his squeaky-clean image, Mr. Cassidy posed nude in a photo shoot for the cover of Rolling Stone in 1972. In the article, he said he was already dreaming about the end of his acting career. Mr. Cassidy was nominated for a Grammy Award for best new artist in 1970, and his 1972 solo album, “Cherish,” went gold. The Partridge Family had six albums achieve that certification from 1970 to 1972.

According to an online biography of the Partridge Family by Ed Hogan, Mr. Cassidy and his co-star and real-life stepmother, the Academy Award-winning actress Shirley Jones, were the only cast members on the television show heard on the group’s records — Mr. Cassidy as a lead vocalist and Ms. Jones on background vocals.

In later years, he wrote books about the toll that stardom had taken on him, and about his struggles with substance abuse. He revealed this year that he had dementia.After watching his mother struggle with dementia, he worked with organizations to educate others about Alzheimer’s disease.

Starting out from New York City

Mr. Cassidy was born on April 12, 1950, in New York City to the actors Jack Cassidy and Evelyn Ward, whose family were among the founders of Newark, New Jersey. They were divorced in 1956 and Jack married Shirley Jones, who also divorced him for his drinking. He died at age 49 in 1976 in a fire at his Los Angeles apartment. Ms. Ward, who like her son was married and divorced three times, died at age 89 in 2013.

He grew up in West Orange, N.J., a suburb of Newark, and his mother and he moved to California when he was still a boy. He struggled in school but began taking small parts in plays and on television, eventually leading to his big break on “The Partridge Family,” which was in substantial part due to his step mother.

In 2001 Donald J. Trump fired him on “The Celebrity Apprentice.”

David, was also married and divorced, this time thrice. His son, Beau, a musician survives him as does his daughter, Katie, an actress; Other surviving family is Ms. Jones, his stepmother and widow of comedian Marty Ingels; and the three half brothers of the Jones-Cassidy marriage: Shaun, Patrick and Ryan.