McCullum, 34, who is playing his 101st and final Test, struck the ball with brutal brilliance to reach his 12th century from 54 deliveries on the opening day of the second Test against Australia at Hagley Oval.
West Indian Richards set the previous record of 56 balls against England in Antigua in 1986 and the mark was then equalled by Pakistan's Misbah-ul-Haq against Australia in Abu Dhabi in 2014.
“I had no idea,” McCullum told a news conference after scoring 145 in New Zealand's 370 all out after they had been reduced to 32 for three in the 20th over on a lively pitch.
“I was trying to hit every ball for four or six. Viv was my idol growing up so it's nice to be able to go past him on this occasion.
“But he was a cracking player, he was an incredible cricketer. I'm almost a little bit of embarrassed to go past him, to be honest.”
McCullum said he knew it was probably going to be his day when he had an “almighty filthy slog” at his second ball which flew over the slips cordon for four.
After scoring 39, he then enjoyed a huge slice of luck when he sliced James Pattinson to Mitchell Marsh who took a brilliant, one-handed catch diving to his right in the gully.
Umpire Richard Kettleborough requested a replay which showed Pattinson had bowled a no-ball.
“I thought it was four as soon as I hit it,” McCullum said. “They do push the front line a little bit. It was quite a nice reprieve. It probably loosens you up a little bit as well, it just relaxes you a little bit more.
“You know you're probably not meant to be out there. You may as well play with a little more freedom.”
McCullum, was greeted by a guard of honour formed by the Australians when he went out to bat with his team already in deep trouble but needing to win to square the two-test series.
He attacked from the start to reach 82 from 48 balls when Josh Hazlewood came in to bowl.
The first two balls were short, preventing him from scoring.
The third was hit over fine-leg for six, the next two went for four and the final delivery was sliced over cover for another boundary to give McCullum the record, which was greeted by a standing ovation from the capacity crowd of 8,000.
“When you are confronted with wickets like that, you know you are going to have to be pretty aggressive,” McCullum concluded.
“I think we got quite a bit of luck today.” – Reuters
Original source: McCullum unaware he broke idol’s record