"Walking Dead" star Steven Yeun says changes are ahead for Glenn Glenn (Steven Yeun), Daryl Dixon (Norman Reedus) and Rick Grimes (Andrew Lincoln) in "The Walking Dead." Gene Page / AMC Lori Grimes, played by Sarah Wayne Callies, in "The Walking Dead." In the ensemble of characters at the heart of AMC's hit series "The Walking Dead," Steven Yeun's Glenn clearly functions as the nice guy. Yes, he's been through the apocalypse just like everyone else, but he seems to be weathering the emotional storm a little bit better than his compatriots - perhaps because he's found love among the ruins of civilization with beautiful Southern belle Maggie (Lauren Cohan). But sitting down for a recent interview in Los Angeles, Yeun cautioned that some big challenges lie ahead for Glenn as Season 3 moves forward and Rick Grimes (Andrew Lincoln) and the gang try to hold the prison from outside interests. "You get to watch his growth as an everyman, but an everyman in his early twenties makes mistakes," Yeun, 28, said of his character's third season arc. Those mistakes can be heavy in this world especially. Now with the addition of Maggie, the stakes are higher because you have another person to account for, you have another person to look out for. "You're going to see him change but in ways that make total sense," Yeun continued. You're going to see him stumble, you're going to see him overshoot, you're going to see him puff out his chest maybe too much and get knocked down. It's been an exciting time professionally for the South Korea-born Yeun, who moved with his family to the United States when he was a young child and initially planned to pursue a career in medicine before discovering a love of performing while attending college in Kalamazoo, Mich. He compared working on "The Walking Dead" set to receiving the best possible on-the-job training in dramatic acting. "I've been very thankful for my growth as an actor over the three seasons," Yeun said. I'm learning every single day. That's rewarding. "Walking Dead: Glen Mazzara on "long-term" plan for The Governor "Walking Dead": Michonne actress talks katana skills "Walking Dead": Audio clip from "Road to Woodbury" "Walking Dead" set: Michonne but no zombies? "The Walking Dead: Escape" is no joke Simon Pegg: George Romero deserves sainthood "Walking Dead": Shane on the "new world order"