Ariel Castro, who kept women captive at his home in Cleveland, Ohio, has died after being found hanging in his cell.
Prison officials said he died in hospital late on Tuesday, after prison medical staff failed to revive him.
Castro, 53, held three women against their will for about a decade until May this year. He kept his victims chained up and raped them.
He was sentenced on 1 August to life imprisonment without parole plus 1,000 years. The house was demolished.
The former school bus driver abducted Michelle Knight, 32, Amanda Berry, 27, and Gina DeJesus, 23, from the Cleveland streets between 2002-04.
A spokeswoman for the Ohio Department of Rehabilitation and Correction, JoEllen Smith, said: "He was housed in protective custody which means he was in a cell by himself and rounds are required every 30 minutes at staggered intervals.
"Upon finding inmate Castro, prison medical staff began performing life saving measures. Shortly after he was transported to [the prison medical facility] where he was pronounced dead at 10:52 pm."
"A thorough review of this incident is under way," she added.
Castro was placed in protective custody because of the notoriety of his case, but was not on suicide watch.
Gina DeJesus was 14 years old when she disappeared. Amanda Berry was 16, and Michelle Knight, 21. Castro also fathered a child with Amanda Berry, who was rescued after she escaped from the house and contacted police.
Ariel Castro was arrested the same day. He was charged with multiple counts of kidnapping, rape and aggravated murder.
At his sentencing, Castro told the court that he had been "driven by sex", adding: "I'm not a violent predator… I'm not a monster, I'm a normal person.
"I'm just sick. I have an addiction, just like an alcoholic has an addiction."
But passing sentence, Judge Michael Russo told Castro there was no place in the world for people who enslave others.
Castro pleaded guilty to 977 charges related to the ordeal of his victims, including numerous rapes and the murder of a foetus because of assaults on its mother.
http://www.bbc.co.uk/news/23955379