He spent his life successfully living up to his self-proclaimed title as "The Greatest." But to Ray "Boom Boom" Mancini, Muhammad Ali was more than just a world-famous boxer, he was a close friend.

"For years he was the most famous face in the world, and for me to get a chance to be friends with him was incredible," said Mancini.

Manicini, says Ali was not only a boxing icon, but a cultural one.

He says he embodied greater battles outside of the ring, including the fights on race and religion.

But when the gloves were on, Mancini says Ali didn't just bring talent to the sport, but a little lip too.

"He was the first one to do psychological warfare; before there was ever a term. He was the one who did it. Calling guys names, we know now he was doing it with a tongue and cheek," said Mancini.

Mancini says the he remembers the last time he saw his friend.  In fact, he couldn't help but smile when recalling Ali's last words to him.

"Last time I saw him he was able to talk a little. The last thing I did, he gave me a hug before I left and he whispered in my ear, 'Stay pretty,'" said Mancini.

And as the world says goodbye to "The Greatest," Mancini says Ali is impossible to replace.

'When they say there will never be another — that truly is. There will never be another. He is the greatest heavyweight of all time. Greatest fighter of all time," said Mancini.