Main, 41, was ordered to serve at least 17 years and six months in prison for killing 55-year-old Francis McGrow - the brother of Tam "The Licensee" McGraw, who died in 2007.
The High Court in Glasgow heard Mr McGrow was stabbed in the back three times by Main, who described himself to police as his victim's best pal.
Then as Mr McGrow lay helpless on the floor of his living room at Hermiston Road, Springboig, Glasgow, Main knifed him a further 37 times in a frenzied attack.
Mr McGrow's heart, lungs and major arteries were all damaged in the savage attack.
No motive for the killing came out in court.
Judge Lord Armstrong told Main: "This was a vicious attack when your victim was lying on his back and unable to defend himself.
"There are no reasons which could possibly justify the taking of another's life as you did. Your release will be a matter for the parole board."
As he was led away to begin his sentence Main waved to members of his family who were sitting on the public benches.
The court heard Mr McGrow was murdered sometime between October 26 and 27, last year.
Main was out on bail at the time and Mr McGrow allowed him to stay in his home.
Main disposed of the knife and tried to hide his jeans which had a fine spray of Mr McGrow's blood on them.
He then travelled into the city and made a call from a phone box in Gallowgate saying Mr McGrow had been murdered.
When interviewed by police, Main tried to claim that Mr McGrow had been the target of an underworld hit because of who his brother was.
Main also told detectives: "Francis was my best pal."
He denied murdering him and said: "I wouldn't murder anybody. It was probably a hit on him. That's it, because of Tam his brother. You know his brother Tam McGraw."
Advocate depute Adrian Cottam, prosecuting, told the court Main had a number of convictions for dishonesty and drugs offences.
Mr Cottam added: "He also has a conviction for assault with intent to rob for which he received a 16-month sentence and assault and robbery for which he received a 26-month sentence."