During a panel at the Paley Center's International Council Summit in New York City Thursday, Plepler was asked what one show makes him go "Oh man, I wish we had that one."
"I'm an unabashed fan of 'Mad Men,'" said Plepler. "You know I love the show. I think Matt [Weiner] is a gifted writer and producer. I was a big fan of the show all through its incarnation."
HBO and Showtime both passed on the series about admen in the 1960s before it was picked up by AMC.
According to a 2009 Vanity Fair article, HBO originally wanted to make the show under the condition David Chase ("The Sopranos") was an executive producer. While Chase "championed the script," he wanted to move away from weekly television.
Is HBO sour about the loss? Plepler says not at all.
"Honest to god, we don't spend time lamenting what we don't have or mistakes," he said. "We spend all our energy and time focusing on, 'What do we want to do now?' 'Who's out there that we want to work with?'"
Plepler added it has been that attitude which led to HBO landing John Oliver on the network.
"Mad Men," starring Jon Hamm and Christina Hendricks, will start the second half of its final seven season next spring.