Memories of an at-times violent childhood - including seeing his mother being "beaten up" by his dad - helped spark some of the destruction powerhouse Jonah Lomu inflicted on the rugby field.

For eight years Lomu was one of the most dominant figures in world rugby - smashing through opponents at will to score 37 tries in his 63 test matches.

Despite debuting in black in 1994, the rugby world first felt the full fury of Lomu during the 1995 Rugby World Cup, including when he he ran over and around England defenders to score four tries in the All Blacks' 45-29 semifinal victory.

And in the warts-and-all feature-length documentary on his life, Anger Within - which will premiere on Sky on Saturday night - Lomu has revealed that some of his ferocious onfield intent was sparked by memories of his upbringing.

"When I used to get angry it was all driven at my dad [Semisi Lomu], more than anything else," Lomu says in the film.

"At times he was the best dad that he could be. It was just when he drank, that's when me and him disagree . . . he was quite violent when he was drunk.

"Mum [Hepi Lomu] was always there to protect the kids. And when Dad got angry and wanted to bash us, she would get in the way and she would get beaten up quite badly, sometimes. That is tough to take. It builds up a lot of things inside of me."

Lomu said that he came from a "religious family". At times when he didn't listen or "rebelled against" Semisi, he said his dad told him that "God himself will punish me, punish me badly".

"I wasn't just physically scarred from a lot of things, but [it] was also the mental games that he played, spiritually really, that was tough," Lomu said.

"I guess that was the thing, that was one of my biggest . . . drivers really to get through things is that when I was playing, when I found it hard, I just thought of my father and that got me through it . . . that anger got me through it.

"I spent most of life fighting with that inside me. It has taken a long time, taken a real long time to be able to come to terms with what my dad was."

For much of his adult life Lomu had little to do with his father. But he worked on repairing the relationship with his dad after becoming a father himself.

The Anger Within captured footage of Lomu, his wife Nadene and their children Brayley and Dhyreille, spending time with a seriously ill Semisi in November 2012, just seven months before Lomu Sr's passing. "I had to rebuild that bridge," he said.

He confided that it was important his two sons had their own memories of their grandfather.

An all-star cast of leading rugby identities feature in the film including Sean Fitzpatrick, Bryan Williams, Waisale Serevi, George Gregan, Francois Pienaar, Philippe Sela, Michael Jones, Sir Gordon Tietjens and Lomu's former manager Phil Kingsley-Jones - the man responsible for helping the sporting great cash in on the Lomu brand.

Talking to Sunday News, Kingsley-Jones described Lomu's adult relationship with his father as "tempestuous". Along with Lomu's first wife, South Africa-born Tanya Rutter, he had tried to encourage the rugby great to reconcile with his dad.

"It was hard. He was certainly not best friends with his father," Kingsley-Jones said.

"His father came in and out of [the] relationship when I was with Jonah. I used to try to encourage him to be closer because I didn't like the idea that I was here doing all this and he [Semisi] was excluded. Semisi would tell me that it was his son, he would remind me of it every now and then."

Both Semisi and Hepi were provided jobs by Kingsley-Jones's management company, Number 11 Management, for a stage of Lomu's test career. Their roles included sorting through the stacks of mail sent to Lomu and posting personalised fan letters from the rugby great.

But Kingsley-Jones said often communication would break down because Lomu felt he had been "let down badly" by Semisi talking to media about his personal life and relationships.

While Lomu spent time cut off from his parents, he become a regular visitor at the Kingsley-Jones family home. "He used to sleep in our house. He would sleep on the settee and be there all day," his former manager said.

"Him and my youngest daughter . . . were like brother and sister. We were all family. He is still like a son to me."

In Anger Within, Lomu speaks candidly of his formative years, revealing the "toughest part" of his childhood was that it was not a "normal childhood".

After being born in Auckland, he travelled to Tonga at the age of 1, to be raised by his aunty. "For five, six years I called her mum," Lomu said.

Lomu takes the film crew to a bridge in South Auckland where he says he used to sleep if he knew he was in trouble with his parents. There were times when he was taken home by police, admitting that some of those he hung out with were now "six foot underground . . . or if not they are in jail".

A turning point for him was the fatal stabbing of a friend in David Lange Park, Mangere, which he visits during the movie with his young family.

He also stressed he was proud of his South Auckland roots. "It's a tough area but I am proud to come from it. I think it made me battle hardened for rugby."

FAMILY DRIVES HEALTH BATTLE

Lomu says the love of his family is driving him in his life and death battle with kidney disease.

The 63-test All Black hero almost died after the kidney transplant he received in 2004 failed in the early stages of the 2011 Rugby World Cup.

Nephrotic syndrome - a serious kidney disorder - ended Lomu's stunning international rugby career in 2002.

In the opening minutes of Anger Within, Lomu has revealed that the three people closest to him were his driving force; his wife Nadene and their sons Dhyreille and Brayley.

"When it starts getting tough that is when I start thinking about my two boys . . . my two boys and my wife. It it sort of gives me a bit of reality again and wanting to live a bit longer," Lomu, aged 38, said in the film.

"It is tough though. For six hours . . . for four to six hours you are stuck to this machine, but you know I guess that is better than the other option which isn't really an option."

Lomu said that he was battling kidney disease as early as 1995, when he took the sporting world by storm with his blockbusting form in that year's Rugby World Cup in South Africa.

Throughout his career, leading up to his final test in 2002, he had tried to hide the seriousness of his illness from successive All Black coaches.

"I did got to the World Cup in 95 and knew that I was sick. And then I had to confirm it to the rest of the world in 96 that I was [ill].

"I was hoping that it would get better but it never did. But you know, I would never change anything. It has made me, me and it has made me a better me too."