[from my original post at Celebutaint]
Norma Jeane had a troubled childhood: she never knew her father, as her mother was widowed but dating around a lot. Allegedly her mother turned insane, abandoning her to a number of foster homes. She was almost smothered to death at two, nearly raped at six. She modeled on and off and signed with an agency. It was at this time that she had her hair cut, straightened, and lightened to golden blonde.
She didn’t find acting work until 1946 when she was discovered by 20th Century Fox. An exec suggested she take the name Marilyn (after Marilyn Miller) as her stage name, since Norma Jeane wasn't considered commercial enough. For her last name, she took her mother's maiden name. She was given minor appearances in 1947, but Fox decided not to renew her contract. She bounced back and forth between 20th Century Fox and Columbia, doing some B movies and small parts. When 20th Century finally gave her a starring role in 1952 with Don't Bother to Knock the reviews were mixed, but they claimed that it demonstrated Monroe's ability and confirmed that she was ready for bigger roles. 20th Century decided to give her a better contract.
Movies like Niagara (1953) launched her as a sex symbol, and proved she could carry big-budget films. Nude photos of Monroe surfaced, and prints were bought by Hugh Hefner. In December 1953, she appeared in the first edition of Playboy, to the chagrin of Fox.
She starred in many successful comedies, such as Gentlemen Prefer Blondes and How to Marry a Millionaire, making Monroe one of the world's biggest movie stars. The extravagant films also established Monroe's "dumb blonde" on-screen persona. In 1955 she married and divorced baseball legend Joe Dimaggio. She filed for divorce on grounds of mental cruelty 274 days after the wedding.
After doing The Seven-Year Itch she wanted serious acting jobs to replace the sexpot image. She went to New York's Actors Studio and underwent psychoanalysis to learn more about herself. Critics praised her transformation in Bus Stop (1956).
She shocked the public when she married playright Arthur Miller. She began fighting with him and falling deeper in to alcohol and drug abuse, as well as a number of affairs. Work on her last picture The Misfits (1961) was interrupted by exhaustion.
In May 1962, she made her last significant public appearance, singing “Happy Birthday” at a televised birthday party for President John F. Kennedy (heightening the rumors that the two were having an affair).
She had a number of projects lined up, but mysteriously, she would never do them. Marilyn Monroe was found dead by her housekeeper on August 5, 1962 in her home in Brentwood; her death ruled as an overdose. Questions remain about the circumstances and timeline of the housekeeper discovery of Monroe's body. Also, some conspiracy theories involve the Kennedy family. There is speculation that her death was accidental but the official cause was "probable suicide".