He shot to notoriety after he imprisoned his daughter, raped her more than 3 000 times and fathered seven children by her.

Now Josef Fritzl is a prisoner himself. The so-called “monster dad” has no teeth, his health is failing and he spends his days doing menial tasks behind bars, Austrian media report.

Fritzl (83) held his daughter Elisabeth captive from age 18 under his house in Amstetten, Austria, telling his wife Rosemarie and police that she had run away with a cult, Spiegel Online reports.

It was only two decades – and seven children – later that Elisabeth’s horrifying ordeal came to an end. In April 2008, Fritzl’s 19-year-old “cellar” daughter, Kerstin (whom he had fathered with Elisabeth) went into a coma and had to go to the hospital.

The girl’s malnutrition and rotten teeth raised alarm and an anonymous tip-off led to Fritzl’s arrest.

He was sentenced in 2009 and is serving a life sentence for murder – for the death of one of Elisabeth's babies – as well as incest, and 3 000 counts of rape, Newshub reports.

Ten years since his vile crimes were unearthed, Fritzl “gets his hands dirty doing jobs at the jail where he is serving a life sentence,” Mirror UK reports.

Fritzl is now toothless after being involved in fights with another inmate, ill and showing early signs of dementia at a prison in Austria, according to Daily Star UK.

“He is said to be extremely unpopular with other inmates and has to be kept in solitary confinement with four guards watching him.”

It’s believed that Elisabeth, now 52, lives in a safe house with her six surviving children and uses a pseudonym.

“Fritzl believes his prison stint is temporary,” Mark Perry, who first broke the story of the crime, told Newshub.

“He still dreams of coming free. That's what the solicitor told me. He still thinks he'll come free one day, go fishing and, and carry on with life.”

Sources: Spiegel Online, Mirror UK, Newshub