Manson and members of his "family" of followers were convicted of killing actress Sharon Tate and six other people during a bloody rampage in the Los Angeles area in August 1969.
Prosecutors said Manson and his followers were trying to incite a race war he dubbed "Helter Skelter," taken from the Beatles song of the same name.
Tate, the wife of director Roman Polanski, was 8 1/2 months pregnant when she was killed at her hilltop home in Benedict Canyon on Aug. 9, 1969.
Victims of Charles Manson
Four others were stabbed and shot to death the same night: Jay Sebring, 35; Voytek Frykowski, 32; Abigail Folger, 25, a coffee heiress; and Steven Parent, 18, a friend of Tate's caretaker. The word "pig" was written on the front door in blood.
The next night, Manson rode with his followers to the Los Feliz home of Leno and Rosemary LaBianca, then left three members to kill the couple.
Manson initially was sentenced to death.
But a 1972 ruling by the California Supreme Court found the state's death penalty law at the time unconstitutional, and his sentence was changed to life in prison with the possibility of parole. He has been denied parole 12 times.
During his four decades of incarceration, Manson has been anything but a model prisoner. Among other things, he has been cited for assault, repeated possession of a weapon, threatening staff and possessing a cellphone.
Officials would not say what Bakersfield hospital Manson is being treated at. But local TV reporters noted a department of prisons van outside Mercy hospital.
For nearly 50 years Charles Manson has been the living personification of evil, a demonic presence captured in scores of photos, each of them marked by his piercing dark eyes and the crude Nazi swastika he carved into his forehead.
"I was thinking today about why Manson is so remembered and such a part of our cultural history, whereas other serial killers have done far worse," said former AP Special Correspondent Linda Deutsch, who covered the 1970-71 trials of Manson and his followers, as well as all of their parole hearings until she retired two years ago.
It was, she concluded, because Manson killed more than just seven people. He also destroyed a Baby Boomer generation's dream of a peace-and-love era that had begun with 1967's San Francisco Summer of Love, two years before Los Angeles' 1969 Manson murders.
"For most of that period, the hippies up in San Francisco and throughout the country really spread a message of love and understanding," Deutsch said. "And now here come these people who wore these hippie clothes and although they were not hippies, they were just people who came together in a commune, they became symbolic of that hippie era.
"In addition to killing seven people, he killed a whole counterculture," she added.
A career criminal and con artist, Manson had reinvented himself during the Summer of Love as a Christ-like figure who attracted young people to a commune he established at an old, abandoned movie ranch on the edge of Los Angeles.
"To tell you the truth, the older I get the harder it is to deal with all of this, to know what I did, how it happened," one of the youngest of his followers, Leslie Van Houten, told a parole panel in September. The panel has recommended she be released, but Gov. Jerry Brown could reject that recommendation as he did once before. No Manson Family member convicted of murder has ever been freed.
Van Houten, now 68, explained how Manson used sex, drugs, repeated playings of the Beatles' "White Album" and readings from the Bible to persuade his young followers that they could launch a race war between blacks and whites by killing people, then hide in the desert until it was over. He was particularly fascinated by the Beatles' song "Helter Skelter," which he saw as predicting the coming race war, although its lyrics mainly seem to reference a childhood playground slide of that name.
His followers' victims included Tate, who was several months pregnant, coffee heiress Abigail Folger and several other wealthy and prominent people.
But what Manson really wanted to do, Deutsch said, was become famous.
At one point he'd befriended the late Beach Boys drummer Dennis Wilson with hopes of becoming a musician as famous as those in Wilson's group. The music industry ultimately dismissed him as crazy and dangerous and, worse yet to his way of thinking, only marginally talented.
"So he wanted to make a statement and be the star that Hollywood wouldn't let him be," said Deutsch. "And he was demonic."