The actor's character Ted Chaough appeared in a handful episodes in past seasons as the boss of a competing advertising firm. But the recent merger of his and Don Draper's (Jon) companies - along with a kiss with Peggy Olson (Elisabeth Moss) - has thrust Ted to the forefront of the 1960s ad world drama.
"I mean Jon's the nicest guy, a genuinely good guy and so he makes it easier ... He's just a good guy. I call it the 'Clooney effect,' when you don't get famous till you're 30 or in your mid-30s."
Kevin also talked about why Mad Men stars keep details of upcoming plots to themselves.
"It's been pounded into us," he laughed. "Matt Weiner (Mad Men creator) gives a speech before every table read and he says 'Welcome. We're really happy to have you here. You're part of the family now and if you say anything we will destroy you.'
"So yeah, he explains the commercial viability of the show is that no one knows. And that's rare these days ... That's what creates the buzz about Bob Benson and Ted and Peggy and Don."