Svengali' figure Baker, who met his wife while working for the Salvation Army, was also living with a third woman, named only as Miss X, who had four children with him over 20 years, who eventually alerted police.
Mr Baker was sentenced to 15 years in jail today for raping the woman, who cannot be named, before allowing friends to do the same while he filmed them.
Caroline Baker had been jailed for three years - but she will only serve 18 months in prison with the remainder on licence.
Eight years after she was taken to Northern Ireland by her captors, police rescued her from the house in Craigavon, County Armagh, in 2012.
Baker, 61, a one-time care worker, is understood Baker met his victim in Britain and either invited or persuaded her to come to Northern Ireland.
When her husband reported her missing in 2004, it seemed she had vanished without trace. And she lacked the mental capacity to escape.
He "paid" his victim Quality Street sweets for having depraved sex with him and others.
He filmed dozens of unknown men raping her in the room then "rewarded" her with boxes of chocolates and sweets if she had been "good".
Because of her diet all but one tooth were completely rotten.
"She told police she did what Baker told her because she was terrified of him but also because he gave her sweets," said a source.
"She even said her favourite was the purple one from the Quality Street box and she would get that if she had been particularly good.
"Medical tests showed she only had one 'sound' tooth and that is why."
Baker and his wife Caroline, 54, prevented her from ever leaving her tiny room by removing the handle on the inside of the door.
The abuse was at their specially adapted home, which consisted of two terrace houses knocked through to make one large home.
Baker's wife Caroline was working as a care worker at a home in Northern Ireland that specialises in mental health residents right up until she was arrested.
The PSNI is understood to have conducted a thorough investigation into whether she may have abused anyone at the home.
Baker was a member of social dating site Badoo where he tried to meet women to satisfy his cravings.
He used the soft and cuddly profile name 'Keiffy Bear' to lure women into his trap.
Throughout police questioning Baker denied the allegations and claimed all the sex was consensual.
Witnesses told police there was always strange men coming and going from the house and after they seized tapes of unidentified men being filmed having sex with the victim, detectives suspected Baker was pimping her out on the internet.
He locked his mentally disabled victim away for years in a tiny room - not allowing her to leave or even see a dentist or doctor.
The room has been decorated since the victim was released from slavery. When she was there the floor was bare and the light didn't work.
When police finally rescued her, she weighed just six stone and her teeth had rotted so badly from all the sweets and lack of dental care she only had one sound tooth.
The sex slave, who's believed to be in her 40s, was only rescued after another woman who, like her, suffered from learning difficulties, raised the alarm when she told a disability support worker that there was another woman living at the house.
The whistleblower, known in court as Miss X, was assessed as suffering chronic post-traumatic stress and said she suffered 20 years of abuse after starting a second family with Baker.
But prosecutors decided there was not enough evidence to prosecute Keith Baker for those allegations.
Both Miss X and Caroline Baker each had four children with Baker and the creepy pad was divided into two sections - one for the women and one for the men.
The victim lived in the squalid half and was allowed to shower only once a week, her 'toilet' was overflowing with human waste.
Keith and Caroline pleaded guilty to a string of horrific sex offences against the single woman who had been living at the property for nearly a decade.
They admitted two charges of engaging in sexual activity with a mentally disabled person and one of enticing her into sexual activity knowing she was unlikely to refuse.
Keith Baker also confessed to six counts of rape of the same woman and a final count of indecently assaulting her.
His wife pleaded guilty to three offences of 'aiding and abetting, counselling and procuring' her husband to rape their victim and a single count of indecent assault.
Baker, who is originally from Guernsey, started his life as a care worker and ended up owning a hotel along with his brother.
Baker groomed his victim in England and, concerned he would be caught by the authorities, decided to take her somewhere they would never look - Craigavon, where his wife Caroline was originally from.
"Baker knew she had been reported missing and so he wanted to get her somewhere 'safe'," said a source.
At a previous hearing the victim was described in court as having severe learning difficulties and in very poor health.
A total of eight children also lived in the house, along with another lady who was another partner to Keith Baker.
The judge said the household was 'highly unorthodox' and the victim was totally isolated from the rest of society.
Her words when she was released from captivity were: "Yes, freedom."
She did not appear on the electoral register, was not with a GP or dentist and never claimed benefits.
Her abusers took material showing Baker having sex with his partner and the victim, almost every time naked, the judge said.
At one stage she was told she had 'learned quite a bit' over the last few years.
She went from being well-nourished to becoming emaciated, extremely thin with a distended abdomen.
The judge commented: 'She did not even know the name of the perpetrator."
When she was released she did not want to be left alone in the room.
Judge Lynch added: 'This is clearly indicative to me of the isolated existence she had led."
She ate everything in a hurry and was dehydrated.
In January 2013 Keith Baker was arrested and claimed he had rescued the victim from an abusive relationship.
He was raised in Guernsey and lived most of his life in Kent. He met his wife when they both worked for the Salvation Army.
He was assessed as displaying sexual deviancy and posing a high risk of re-offending.
Caroline Baker played a 'secondary' role, the judge said, influenced by her husband's domineering personality.
"Caroline Baker was in a virtual state of marital captivity."
He said she was a pawn under the influence of a very powerful and dominating Mr Baker and also a victim of exploitation and emotional control by her husband.
When questioned she claimed the woman was the "most sensible person I know" and claimed the sexual activity was initiated by her.
