He was known as the Dark Destroyer in his boxing prime, but now Nigel Benn is concentrating on building people up, not knocking them down – though he hasn't turned his back on the sport.

Benn, an army veteran who served in Northern Ireland during the Troubles, was one of the most successful British boxers ever. He became the WBC and WBO super middleweight champion, with a record of 42 wins from 48 fights, including two knockouts.

However, 20 years ago a fight against American boxer Gerald McClellan ended disastrously. Benn won the fight – described by boxing journalist Hugh Mcilvanney as "relentless, mutually destructive aggression...one of the most brutal fights any of us at ringside had witnessed" – but McClellan was left with brain damage and confined to a wheelchair. Benn subsequently raised large amounts of money to help pay for his care.

He left boxing not long afterwards and went through a troubled period in his life, famously describing himself as "Satan's right hand man". He drank, took drugs, suffered from depression and attempted suicide one night in his car. The death of his older brother, who died in unexplained circumstances when Benn was only eight, was a continuing shadow over his life.

He and his family moved to Australia after several years living in Spain at the suggestion of his wife Carolyne, where they attend Hillsong Church. In a Sydney Morning Herald interview, Benn recalls the moment he "said the prayer of salvation": "All my addictions from drink, from sex and smoking weed it [clicks his fingers] all went like that. I was set free from everything." He has attended Hillsong College and is using his boxing skills to mentor other would-be fighters – including his promising son Connor.

He told the Guardian: "My new drug is serving people whether its through boxing or in my role for Hillsong as a volunteer assisting people with their marriages or helping those less fortunate.

"I'm great friends with an 80-year-old woman whose lawn I cut and do odd jobs for. It's a required part of the service."

He added: "I won two world titles and filled Old Trafford, owned a Bentley and a mansion, had tea at Buckingham Palace, DJ'd at Ministry of Sound, served proudly in the British Army and here I am cutting the grass of an 80-year-old woman. And lovin' it. I look at my life now and I feel blessed, no more drugs or smoking, I'm fittest I've ever been. Look at my family. I can't ask for more."