She was born on 1 June 1926 in the Los Angeles County Hospital, the third child of Gladys Baker. She lived with a number of foster parents, as her mother was mentally unstable, until her mum's best friend Grace Mckee became her guardian.
Mckee was inspired by Jean Harlow and allowed the nine-year-old Norma to wear makeup and curl her hair until McKee married and sent Norma to an orphanage.
She was then sent to live with her great aunt Olive Brunings and it is thought that Norma was sexually assaulted by Olive's son, which some biographers have claimed led to her later behaviour, including substance abuse.
At 16, she escaped her old life by marrying a 21-year-old aircraft plant worker, Jim Dougherty, who she divorced four years later. By this time she had begun modelling bathing suits and, after bleaching her hair blonde, posed for pin-ups and glamour photos.
Howard Hughes tried to get her a screen test but was beaten to the punch by 20th Century-Fox, who signed her to a contract - at $125 per week for six months - and changed her name to Marilyn Monroe.
After appearing in small parts in films including 'Love Happy' and 'All About Eve', Monroe found fame in 1953 with 'Niagara', 'Gentlemen Prefer Blondes' and 'How To Marry a Millionaire'. That same year, she began dating baseball player Jo DiMaggio, and a nude spread of her appeared in the debut issue of Playboy magazine. Monroe had hit stardom.The nude spread caused a scandal with her studio so she agreed to admit she had posed for the photo as she was struggling to pay her rent. The resulting publicity created some sympathy for the struggling actress.
In 1954, she eloped with DiMaggio - a union which was only to last eight months - before filming 'There's No Business Like Show Business' and 'The Seven-Year Itch', with the classic scene in which she stood over a subway grating, skirt billowing. She applied for divorce from DiMaggio on the grounds of mental cruelty. Despite this, he secured her release from the Payne Whitney Psychiatric Mental Clinic in 1961.
Monroe's work began to slow down but, after undergoing psychoanalysis, critics praised her acting in 1956 film 'Bus Stop'. She married playwright Arthur Miller the same year, divorcing him four years on. In the meantime, she fell prey to alcohol and pills, and suffered two miscarriages.
After a year off in 1958, Marilyn returned to the silver screen for smash comedy, 'Some Like It Hot'. In 1960, she appeared in 'Let's Make Love', with Yves Montand, with whom she had an affair.
'The Misfits', written by husband Miller, was to be her final film. Work was interrupted by exhaustion, and she was then fired from 'Something's Got to Give' for not turning up for filming.
On 19 May 1962, the actress attended the early birthday celebration of John F Kennedy at Madison Square Gardens and sang 'Happy Birthday Mr President' in a now iconic manner.
She went into seclusion and on 5 August 1962, she was found dead at her home of an overdose of sleeping pills, aged 36. The verdict was suicide but has always been disputed, with countless conspiracy theories triggered by alleged affairs with brothers John F and Robert Kennedy.
Monroe has been portrayed by a number of actresses over the years, with the latest being Michelle Williams.
Williams will be playing Monroe in the BBC TV film 'My week with Marilyn' this year (2011), which portrays the seven days Monroe spent in England in 1957 filming 'The Prince and the Showgirl' with Laurence Olivier.