The vast majority of the 350 or so inmates serving life are murderers, but a few prisoners' crimes were so shocking they got the maximum sentence available to the courts.
Thomas Stokes, from Newbridge, Co Kildare, was 36 years old when he became the first person to get a life sentence for rape in 1996.
Along with another man, Stokes picked up a vulnerable 20-year-old woman on the streets in Dublin.
He drove her to the Wicklow mountains where he subjected her to a depraved two-and-a-half hour sex attack on a lonely road.
The woman said in her evidence: "He told me to shut up or he'd bury me."
"I told him I wanted to go home to my kids and mother. He kept calling me a tramp. I thought I'd never see another face again."
At one point Stokes stopped for a cigarette and then continued the attack.
It emerged Stokes had previous convictions, and had received a four-year sentence for sex assault in 1984 and six years in 1989 for threatening to kill his wife after pouring petrol through her letterbox.
Meath native and serial rapist David Geraghty, now aged 56, got an indeterminate sentence in the UK in 1998 for the rape of a 22-year-old hitchhiker and the attempted rape of a pregnant 16-year-old.
It emerged during his trial he had been jailed in Ireland in the 1980s for four years over seven sex attacks, including rape.
He had moved to the UK and had married a woman who had no idea of his sordid past.
The trial judge in the UK had commented: "I have come to the conclusion that the nature of the offences coupled with your history indicates that you are a person of unstable character likely to commit similar offences in the future."
David Power was 25 when he launched at attack on a woman at a Supermacs restaurant in Nenagh in January 2007.
She had been on her way home from a nightclub with her boyfriend when she stopped at the restaurant to use the toilet.
She was pushed inside by a man who grabbed her by the shoulders and turned her around as she opened the door of a cubicle.
Her cries for help could not be heard above loud music in the toilets as Power raped her.
He had previously been jailed in 2001 for two other sex attacks in Cork city.
One of those victims told the trial judge at the time: "He is an evil man who I have no doubt will re-offend. I want justice for what he has done to me and to prevent it from happening to another woman.
"I would like to see him sent to prison forever."
A number of rapists have successfully won appeals against life sentences for their crimes, but the man known as the Athlone Rapist is not one of them.
The man, who can't be named for legal reasons, lost his appeal in 2015 after getting the maximum sentence for a sex attack in which he lured two young girls from a children's house party.
He had told them his daughter was too shy to come out to play with them and brought them to a derelict house.
He threatened to slit the throats of the six and nine-year-olds and their parents as he raped them a number of times before they escaped through a window.
Even though he pleaded guilty and co-operated with gardai Judge Peter Carney said the offences were too serious to consider a reduction in the maximum sentence.
Eric Daniels, now aged 38, also failed in his appeal against a life sentence for the attempted murder of a ten-year-old girl in November 2001.
Daniels from Clonmel, Co Tipperary, had admitted attempting to murder the girl in a field in Clonmel because he "wanted to see what it was like to kill somebody".
He was 18 when tried to murder the girl because he "wanted to inflict pain".
Daniels said he tied a lace from his Doc Marten boots around the child's neck and tightened it after luring her into the field on the pretext of showing her some puppies.
The young victim testified via video-link that she thought she was going to die when Daniels put the lace around her neck, tightened it and tried to choke her.
She escaped after playing dead.
Michael Murphy was given a life sentence for viciously assaulting and raping a tourist in a Dublin hotel after being invited back to a hotel room with her friend in March 2007.
As the woman was later was showing Murphy to the door, he suddenly launched a violent assault and threatened to kill her.
She eventually ran naked and screaming from the room after her friend awoke and had also run into the corridor shouting.
Murphy had previously been jailed indefinitely in the UK in 1994 for raping a woman and killing her by stabbing her 33 times.
He was detained in a secure mental institution in Manchester until his escape in 2006, less than a year before he raped the woman after meeting her in a pub in Temple Bar.
In 1975 the Mayo native was convicted of the manslaughter of his father, described as a violent alcoholic, and was given an 18-month suspended sentence.
The trial judge, George Birmingham said Murphy was "a highly dangerous man whose threat to society is ongoing".
He said a life sentence for rape was unusual but these were exceptional circumstances because he was at large for "a truly appalling rape".