Retired heavyweight Frans Botha faced the best of the best in his pro career - including Mike Tyson, Evander Holyfield, Lennox Lewis, Michael Moorer, Wladimir Klitschko and several others.

He actually captured the IBF heavyweight title in 1995, but the contest became a no-contest after Botha came up positive for steroids in a post-fight drug test.

Botha retired in 2014. In his second to last career bout, Botha was knocked out in two rounds by a 5-0 rising prospect from New Zealand, Joseph Parker.

Since their bout, Parker (24-0, 18 KOs) has grown by leaps and bounds - and became the WBO heavyweight world champion.

Parker was last in action back in September, when he won a twelve round majority decision over mandatory challenger Hughie Fury.

Three years since their bout, Botha believes Parker is fully capable of unifying the entire heavyweight division.

"I had a lot of fun with Baby Joseph though he's not a baby any more, he's world champion. I said then he's got the speed and when the power comes he's going to be the unified world champion," Botha said to Fairfax Media.

"With his speed and power, I believe this kid is like Muhammad Ali. Don't underestimate him. I see a lot of things happening for Joseph Parker. The sky is the limit for him. It's all up to him.

"I think the level of the division is getting back to where it was, there are some exciting guys. Joseph Parker is popular, he has charisma, he has the right team behind him. He has to keep doing what he is doing ... keep building and getting around."

Botha says it is very important for the heavyweights to find a unified champion

"100 percent ... you have all these alphabetical titles, but there are the four main recognised titles. Joseph has one of those. I think you need to unify those four into one champion," Botha said.