I've heard his name numerous times on the forum, but sad to say I still don't really know who he is. He's made some wild predictions about bitcoin, correct? Did he make a specific prediction that was supposed to have come true by now?
MacAfee is the man who made a very popular antivirus software and firewall in the 1990s. He left the company that bears his name in the mid 1990's and then moved to Belize where he appeared to go batshit (posting videos of himself snorting coke onto youtube and so on).
I think he managed to lose a fortune of about $100 million on living a wild life and then started shilling for dubious alt coins, and of course making wild predictions about bitcoin.
Basically everyone should ignore him - whatever brains he had have been well and truly fried by now.