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At first thought, that stick-thin party person Amy Winehouse might seem to have little in common with a matronly, intensely shy woman who stayed at the top for half a century without a whiff of scandal. But like other young vocalists – Jamie Cullum, Madeleine Peyroux – Winehouse acknowledges a debt to Ella Fitzgerald. “With my school-friends I listened to hip-hop and Missy Elliott, but jazz was my private thing. From the age of 11 I was listening to Ella. I loved her.”

April 25 would have marked Ella Fitzgerald’s 90th birthday and for her record company that’s excuse enough for a season of rereleases, a glitzy tribute concert in LA, and an all-star album, We All Love Ella. Its contributors are effusive. Diana Krall calls Fitzgerald “the greatest improviser, jazz scat singer – a complete natural”. k.d. lang describes how she was 20 when she bought her first Fitzgerald record and “studied it and studied it”. Natalie Cole remembers A-Tisket A-Tasket as the first song she learnt, aged 7.

Fitzgerald recorded that nursery tune in 1938. It sold a million copies and she went on to enjoy the longest career at the top of any 20th-century American singer. By her last show in 1991, she had sold 40 million records.

If her contemporaries Billie Holiday and Sarah Vaughan are remembered as great vocal interpreters, Fitzgerald was the surest, steadiest talent. Her clear, melodic voice stayed faithful to the notes on the page and her versions of the Great American Song-book usually became definitive. “I didn’t realise our songs were so good until Ella sang them,” said Ira Gershwin.

But, perhaps because her personal life wasn’t grimly dramatic, she doesn’t attract the fascination that Holiday still does. Lady Day teetered from childhood neglect and prostitution to abusive relationships and drug addiction. Infamously, on her deathbed in 1959 she was arrested for heroin possession. To her body were taped 15 $50 bills, advance payment for a series of autobiographical articles. Her bank account contained 70 cents.

Holiday’s singing has a bittersweet melancholy, but Fitzgerald was always upbeat. Billie sang the blues; Ella swung. Not that Fitzgerald’s life was easy. Born to poor parents, she was orphaned in her mid-teens. The tall, gawky girl was then shuttled between Harlem foster homes and relatives’ flats, often running away. Fitzgerald had hoped to be a dancer before winning an amateur night at the Apollo Theatre by singing a Hoagy Carmichael tune. She had aimed to hoof until a last-minute attack of nerves. The prize was supposed to include a week’s cabaret work but the organiser refused, citing her slovenly appearance. The bandleader Fletcher Henderson would also refuse her work because of her looks. But when finally taken on by Chick Webb, her star rose remorselessly. Over her career she would record a remarkable 200 albums.

Like other black artists, Fitzgerald lived with the daily brute realities of racism but would receive help from an unlikely benefactor – Marilyn Monroe. In the 1950s the star lobbied the owner of the fashionable Mocambo night-club in Hollywood to allow Fitzgerald to become the first black artist to play there. Monroe pledged that she would be at a front table every night. “After that I never had to play a small jazz club again,” said Fitzgerald. In 2005 Bonnie Greer turned their (undocumented) meeting into a play, Marilyn and Ella Backstage at the Mocambo.

For all the success, Ella was an intensely private woman who had two short marriages. Greer believes that, like Monroe, she was lonely, any relationship hampered by an exhausting work schedule.

The drummer Ed Thigpen, who toured with her from 1967 to 1972, says: “The stage was her life. The public were her family. When she sang ‘People who need people’ she meant every word.

“She was shy until she got to know you, but then she opened up. She was meek in some ways, strong in others. As a woman – and particularly a black woman who was one of the first to cross the colour barrier in entertainment – she had to be tough.”

Biographers talk of how Fitzgerald relaxed by watching TV soaps or curled up with a book. Thigpen remembers a wilder time. “We’d go disco-dancing. She was a big Tom Jones fan and she could dance her head off.”

Fitzgerald did not need to work as much as she did. Her manager, Norman Granz, made sure that, unlike Holiday, she was well rewarded. But Thigpen knows what kept her going. “The first time I went to Japan, the applause and adulation before she had even sung a note was one of the most moving experiences I’ve ever had. And it kept coming for her.”

After Fitzgerald died, aged 79, from diabetes at her Beverly Hills home, the columnist Frank Rich wrote about the importance of her classic “songbook” albums dedicated to the work of the Gershwins, Rodgers and Hart and Irving Berlin. She had “performed a cultural transaction as extraordinary as Elvis’s integration of white and African-American soul. Here a black woman popularised urban songs often written by immigrant Jews to a national audience of predominantly white Christians”. Johnny Mathis simply declared: “Among all of us who sing she was the best.” Also, if that’s how you want to judge her, she had a lot more than 70 cents in the bank.

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