Left Brain is a member from the alternative hip hop collective Odd Future Wolf Gang Kill Them All (OFWGKTA).
He is the producer and backing vocalist of MellowHype, a duo he forms with rapper Hodgy Beats.
This guy was made famous around the web after he got pictured looking literally like a thumb.
This is actually amazing, just google image it.
Used sometimes when one of your friend looks like him on a picture, or to describe any fat bold guy.
Never heard of the human thumb? Check him out, this guy's awesome.
Haha you look like the human thumb on this picture!