McCullum, in his final Test for New Zealand, took just 54 balls to reach his century, two deliveries quicker than Richards when he first set the record.
Richards’ innings from 56 balls came against England in 1986 and was equalled by Pakistan captain Misbah-ul-Haq in 2014.
And while coaching the Quetta Gladiators in the Pakistan Super League, Richards took time out to pay tributte to the retiring McCullum.
“Let me take this opportunity to congratulate Brendon, I’ve been a great fan of your for many years,” said Richards in the video message.
“If there was anyone who you’d have like to surpass whatever you achieved, it would be you.”
McCullum had earlier said he was “embarrassed” to break the record of his childhood hero.
“Viv was my idol growing up, he was an incredible cricketer. I’m almost a little bit of embarrassed to go past him, to be honest,” said McCullum.