What's the deal with Joe Rogan being a "Gateway to the Alt-Right"?

After seeing this post I asked a friend if he knew who Joe Rogan was so I could show it to him. He said that the only thing he knows about Joe Rogan is that he's considered the gateway to the alt-right.​Is this right? I only know him for interviewing a few interesting people. via /r/OutOfTheLoop http://bit.ly/2Hy1rkV