Andrew Lincoln, The Walking Dead

As The Walking Dead's short but highly celebrated first season comes to a close, series star Andrew Lincoln still can't quite wrap his head around the massive success of the AMC zombie drama.

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"I don't think any of us expected this. In our best-possible-case scenarios, this isn't even close," the British actor tells TVGuide.com with a laugh. "It feels really unprecedented because the response has been so positive and affectionate. It's amazing. When you make something, you just hope that people will get why you wanted to do it or what you got from the script. But I don't think I've ever felt such an extraordinary reaction [where viewers] got what we intended to make. It feels great."

As Sheriff's Deputy Rick Grimes, Lincoln is both the leader of the show's ensemble and the misfit band of survivors who have banded together after the zombie apocalypse. "I think initially, everybody looks to a uniform," Lincoln says of why his character has quickly become the man in charge. "This is a crisis situation, so even before Rick entered the camp, Shane [Jon Bernthal] was the leader because he [was also a] lawman. They're the marker point for society."

But throughout the season, Shane has increasingly challenged Rick's decisions, perhaps because Shane also quickly developed a relationship with Rick's wife, Lori (Sarah Wayne Callies), who believed her husband was dead. In the penultimate episode, for example, Shane argues that the camp should move to a military base for safety rather than travel into Atlanta to visit the Centers for Disease Control and Prevention, as Rick suggests. The camp ultimately sides with Rick.

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"There is a struggle for power and a conflict of interest, but ultimately there is still a deferral in place," Lincoln says of Rick and Shane's relationship. "But I do think it's only a matter of time before that starts to get challenged again."

Indeed, in Sunday's finale the survivors will meet a CDC researcher, Dr. Edwin Jenner (Noah Emmerich). And although he offers the group hot showers, booze and some explanations about how exactly the zombies come back to life, the group's outlook isn't rosy.

"They're obviously looking for safety and some answers, and they think they potentially have salvation," Lincoln says. "And then over a couple hours they realize this man isn't who they think he is. They realize extremely quickly that they may be in more fear of their life being in the CDC."

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Since Rick led the camp to this fate, will his judgment be more readily questioned in the future?

"I think so," Lincoln says. "The great thing about the world that they inhabit is that there are no right answers, there are no right decisions made. Everything seems to be a compromise at the moment, and it's just about how good a compromise you can make.

"The fascinating thing about this group dynamic is that it's constantly changing," he continues. "In one episode, a person can be the villain and in the following episode they can be the savior."

Lincoln says what ultimately makes Rick the best leader is his integrity. And even though Lincoln acknowledges the dark journey that's been mapped out for his character in the comic book series that inspired the show, he believes the series won't focus on that "erosion" right away.

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"People tune into his moral center," Lincoln says. "They know that his first responsibility is his wife and son. They say he's a good man. So they have that to hook into and trust. I think ultimately it's all about trust.

"I do want to see this erosion over the years that I play Rick," he says. "The rules have changed, the world has changed, so your moral center has to develop with it. Decisions are not as clear-cut as they can be in the civilized world, and that's the fascination for me: how you maintain your humanity in this inhumane place."

The Walking Dead finale airs Sunday at 10/9c on AMC, preceded by a marathon of the entire first season beginning at 4:30/3:30c.