For the first half of the 1970s, the Osmonds enjoyed the kind of pop-idol adulation enjoyed by the Beatles or the Jackson 5. Raised in a devout Mormon household, the Osmond siblings combined a formidable collective work ethic with an extraordinary amount of natural talent. Alan Osmond, who has died aged 76 after suffering from multiple sclerosis since the late 80s, made crucial contributions to the group as songwriter, musician and producer. He co-authored many of their biggest hits, including Down by the Lazy River, Hold Her Tight and Wild Horses.

In a social media tribute, his brother Donny wrote that “Alan was our leader in every sense of the word. His tireless work helped build everything we became … I owe him more than I can ever fully express.”

The third of the nine children of George Osmond Sr (a postal worker and second world war military veteran) and his wife, Olive (nee Davis), Alan was the oldest member of the Osmond family singing group. They all grew up in Ogden, Utah, as congregants of the Church of Jesus Christ of Latter-day Saints (Mormons), and gained their earliest musical experiences with the church choir.

Alan’s older brothers Virl and Tom were both born with badly impaired hearing. In the TV film Inside the Osmonds (2001), the group explained how they originally performed to pay for hearing aids for Virl and Tom, as well as to raise funds for Mormon church missions. In 1958 Alan joined his brothers Merrill, Jay and Wayne to form a barbershop quartet, and they performed regularly as the Osmond Brothers at state fairs in Utah before a visit to Disneyland in California earned them an audition with Walt Disney. This resulted in a fateful television appearance in 1962 in Disneyland After Dark, an episode of Walt Disney’s Wonderful World of Color that also featured Bobby Rydell and Louis Armstrong.

Their performance was spotted by Jay Emerson Williams, the father of the singer Andy Williams, which led to them being invited on to The Andy Williams Show on NBC TV, where they made more than 60 appearances over five years from 1962. “That launched us into our career on TV,” Alan commented. In 1963, six-year-old Donny Osmond made his debut appearance with the group on the show. After a detour to The Jerry Lewis Show in 1968, they returned to Williams’s programme in 1969. Williams commented that “They knocked us all out, they were terrific.”

However, as the 70s loomed, the Osmonds’ groomed and wholesome style began to look outmoded, as the creative boundaries of rock and pop music continued to expand. The brothers scored their first chart hit, and first No 1, with One Bad Apple (1970), an infectious slice of pop-R&B reminiscent of the Jackson 5, who had turned down the song for themselves. The song was written by George Jackson (no relation to the eponymous pop stars), but the Osmonds now began to focus on their own writing and musicianly skills. Alan played piano and guitar, as well as co-producing and co-writing with Merrill, sometimes in collaboration with Wayne and Jay.

They wrote Down by the Lazy River, a No 4 hit in 1972, and enjoyed further self-penned successes with the funky Hold Her Tight and the hard-rocking Crazy Horses, the latter earning high praise from Black Sabbath’s Ozzy Osbourne. Both of these reached the US Top 20, with the latter ascending to No 2 in the UK. They scored further UK successes with Goin’ Home (No 4) and Let Me In (No 2), with 1974’s Love Me for a Reason, written by Johnny Bristol, reaching the top spot (Boyzone’s cover of the song reached No 2 in the UK in 1994).

As the 70s wore on, Osmondmania began to falter and the group fell out of favour, not least because of the failure of the album The Plan (1973). This was an attempt to explore their Mormon beliefs in song, with the album title referring to the religion’s Plan of Salvation; while it spun off the UK hits Goin’ Home and Let Me In, the reception in the US was lukewarm, with the album failing to reach the US Top 50.

All the songs were written by Alan, Merrill and Wayne, and broke new ground for the group by using synthesisers and incorporating prog-rock style elements. On the track Movie Man, Alan even essayed a rare vocal performance. He considered the disc to be a magnum opus conceived to emulate the creative heights of the Beatles’ White Album, although not everyone agreed.

However, the Osmond family baton was now picked up by siblings Donny and Marie, who both went on to develop significant solo careers as well as hosting their own TV programme. Alan became one of the producers of the Donny & Marie show, which ran on ABC-TV from January 1976 to May 1979. In Britain, it aired on BBC One on Sunday afternoons, billed as The Osmonds. The youngest Osmond, Jimmy, achieved considerable success in music, TV and musical theatre, having got off to an early start with his UK chart-topper Long Haired Lover From Liverpool in 1972. At nine years and eight months, he was the youngest performer to have a No 1 hit in Britain.

The 70s ended disastrously for the Osmonds, as they found their collective fortunes (estimated at $100m) almost wiped out by a combination of poor business decisions, financial mismanagement and fraud. However, rather than declaring bankruptcy, they set about clearing their debts by performing live shows. In 1982, Alan rejoined his original Osmond bandmates Wayne, Merrill and Jay to make a comeback as a country music band. “Country music really is the backbone of America,” Alan said. “It doesn’t just come and go. And we’re kind of flag-wavers. You find that in the country area, too.” The new approach earned them a couple of hits on the US Country chart with I Think About Your Lovin’ and It’s Like Falling in Love (Over and Over).

In 1987, Alan was diagnosed with multiple sclerosis, but he was able to continue performing until 2007, when the group passed its 50th anniversary. In October 2019 he joined the original Osmonds quartet in a farewell performance on the CBS TV show The Talk, co-hosted by Marie, who had just turned 60. They performed a specially written song, The Last Chapter, as a “thank you” to their fans. In 2024 Alan published an autobiography, One Way Ticket.

He is survived by his wife, Suzanne (nee Pinegar), whom he married in 1974, their eight sons, Michael, Nathan, Doug, David, Alex, Jon, Scott and Tyler, his brothers, Tom, Virl, Merrill, Jay, Donny and Jimmy, and sister, Marie.