(CNN) -- Legendary singer Andy Williams, known for his smooth voice and classics such as "Moon River," died after a year-long battle with bladder cancer at his Branson, Missouri, home Tuesday night, his family said.

Williams, 84, began his singing career as a child in a quartet with his brothers, but he rose to stardom as a solo act starting in the 1950s.

"The Andy Williams Show," a weekly television variety program that ran for nine years on NBC starting in 1962, and a dozen TV specials from 1959 through 1987 made Williams a household name in the United States.

He spent the last 20 years of his career performing on his own stage at his Moon River Theatre in Branson.

Jimmy Osmond said his family would be "forever grateful for the interactions we had with him."

"Not only did he discover us as a group, but also allowed us the opportunity to be discovered as individuals and develop our own talents," Osmond said.

"The clarity and warmth and grace of his singing shaped my love of music as I watched my brothers perform with him on his weekly show," Donny Osmond said.

Williams gave him several voice lessons when he was just 7, Osmond said.

"When I finally joined my brothers and toured with Andy as his opening act and back-up singers, I was always impressed with the way he handled an audience," he said. "He loved the audience. That was one of the most important lessons he taught me."

His sister, Marie Osmond, who made her TV debut on his show at age 3, said Williams was "the first person to affect my career."

"The group 'The Osmonds' would not exist without the foresight and generosity of our mentor Andy Williams," Marie Osmond said.

"No one sang more beautifully than Andy Williams," she said. "Hearing his version of 'Moon River' never failed to move me deeply. I can't imagine the holiday season without Andy Williams; we did so many specials together."

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"Moon River" became his theme song after he performed it at the 1962 Academy Awards, where it won an Oscar for best song in a movie. Audrey Hepburn sang the Johnny Mercer and Henry Mancini composition in the film "Breakfast at Tiffany's."

Williams' recording career reached superstar status in 1963 when his album "Days of Wine and Roses" spent 16 weeks at the top of the U.S. music charts.

His variety TV show, which promoted the careers of many other artists including the Osmonds, won high ratings and three Emmys.

Singer Ray Stevens, who was managed for years by Andy's brother Don, called him "one classy guy."

"He was a marvelously talented and generous performer who in 1970 entrusted his nationally acclaimed TV show and audience to a green kid from Georgia," Stevens said. "That kid was me, and he changed my life."

Williams hosted the first live Grammy Awards telecast at the Hollywood Palladium in 1971. He went on to host for seven years straight.

"The entertainment industry has lost a giant piece of its living history today, but Williams' legacy will forever be enshrined in the annals of music and television," said Neil Portnow, the president of the National Academy of Recording Arts and Sciences. "Our deepest condolences go out to his family, friends, and all who will miss this American treasure."

The singer hosted five Christmas television specials, between 1973 and 1985, along with seven other television specials, the first in 1959 and the last in 1987.

Williams, who also had a home in La Quinta, California, is survived by his wife of 21 years, Debbie, and his three children with French singer Claudine Longet -- Robert, Noelle and Christian.

He was married to Longet from 1961 until their divorce in 1975. A year later, she was charged with the fatal shooting of her boyfriend, Olympic skier Spider Sabich.

Williams stood by Longet, who claimed the shooting was accidental. She spent a month in jail.

Williams' Branson theater was the first non-country venue built in the small Missouri tourist mecca.

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He was born on December 3, 1927, in Wall Lake, Iowa, where he began singing with brothers Bob, Dick and Don in a Presbyterian church choir led by their parents.

Williams was just 8 when he made his professional singing debut with the Williams Brothers Quartet. The brothers were regular performers on radio station WHO's "Iowa's Barn Dance Show" in Des Moines. Their popularity grew, taking the brothers to national stations, including WLS in Chicago and WLW in Cincinnati.

Doris Day was his friend when they were both young and living in Cincinnati.

"He and his brothers sang and, of course, so did I, and often I would go over to their house and we would sing together," Day said Wednesday. "They asked me to join their group, but my vocal coach thought I should be out on my own, and so that's what I did."

Smokey Robinson said Williams "befriended me when I was just a teenager starting out in show business, and we remained friends throughout the years."

"I regret that we didn't have the chance to spend more time together," Robinson said. "He was one of the great voices and great people of our time."

Howard A Williams