Johns said he'd known Sir Peter for 16 years and made the trip from Australia especially for the opening.
"I remember running into this [guy] in 1995, and thinking, 'Who is this madman? Over 16 years - it doesn't matter he's been knighted and sold his businesses and made some money - he's still the same person. That's what I love about him."
Johns paid tribute to Sir Peter's charity work, singling out the way he'd raised cash and flown a large number of Christchurch fans up to Auckland for a Vodafone Warriors game as a break from their earthquake-devastated city.
"It's what the Butcher does; he cares about people and he's giving back to the community. He's a special person."
An NRL sports commentator now, Johns donated a pair of boots to the museum and joked he'd worn them plenty of times to beat the Kiwi league team during his career. He tipped the All Blacks to win the World Cup on Sunday.
Mr Glenn said every country needed a Mad Butcher, and former Kiwis coach Graham Lowe said the museum was an excellent asset for the area.
Sir Peter said he hoped the museum would become a top tourist attraction in Auckland. "This belongs to New Zealanders, they own this. I've bequeathed the whole thing - the contents - to New Zealanders."
But it wasn't for boffins, he said; instead it was for the everyday person.