"A 'showrunner' as a position is a relatively new thing. It used to be the executive producer. That's not true anymore. Now it’s evolved into this model where people look to showrunners and say, that guy is that show. It’s just become a lot more interesting to know the showrunner and to get a sense of that person. It’s certainly not true of every show on television. But if you meet [Mad Men creator and producer] Matt Weiner, he looks like Mad Men, he sounds like Mad Men, Matthew is Mad Men, he just is." - Matt Nix
Check out the whole interview at Deadline Hollywood.