Ray Richmond contributes to Deadline’s TV coverage.

The Walking Dead is anything but. The AMC drama is to zombie entertainment what Krispy Kreme is to fried dough: an instant sensation. It broke from the gate in October 2010 and immediately established itself as the most-watched hour on cable, dwarfing the numbers of its esteemed AMC stablemates Mad Men, Breaking Bad and The Killing. It earned a Golden Globe nomination for top drama series and landed four Emmy noms in 2011, winning for its prosthetic makeup.

And yet The Walking Dead arrived last fall needing to prove itself all over again. Why? Because in late July it parted company with its revered creator, exec producer and showrunner Frank Darabont, who was replaced by his head writer and second-in-command Glen Mazzara. Would it be the same show without the three-time Oscar-nominated filmmaker crafting the storylines, steering the ship and calling the shots? AMC held its breath, as did the legion of fans of the comic book/graphic novel series from Robert Kirkman on which the series is based.

Then the numbers came in: Nearly every week during both halves of its second season, The Walking Dead seemed to shatter demo ratings records for cable. The premiere in October averaged 7.3 million total viewers (up from 5.4 million the year before). That rose to 8.1 million for its midseason kickoff in February. By the time the finale rolled around in mid-March, the number soared to 9 million viewers, 6 million of them adults 18-49. It now ranks as the most-watched basic cable drama ever in the 18-49 and 25-54 demos and is No. 3 all-time in total viewers trailing only USA’s Monk and TNT’s The Closer.

So much for any chaos behind the scenes decimating the product on screen.

If the transition to the Mazzara era was shockingly smooth, however, that was hardly an accident. In choosing Darabont’s first lieutenant, AMC was putting its money on an unflappable alum of FX’s The Shield who quickly understood that staying the course was the best policy.

“The particular challenge when I became showrunner was to convince the cast and crew that we were still going to follow the plan that Frank and the writers and I had developed together,” Mazzara said. “It was really about fine-tuning what was already in the can. I realized we already had a good direction going and we should keep moving that way, not throw the baby out with the bathwater.”

Another test for Mazzara was walking the high wire between Walking Dead’s three competing elements: high-end character drama, graphic novel source material, and horror. “It’s a matter of always keeping those three in balance,” he believes. “I think by the end of Season 2, we were able to bring those things into better balance than we’d been able to before that. There were times, for instance, when the horror fans became frustrated. But I think we hit our stride during the last episodes of the season and found the right tone. And going forward to Season 3, I think the pacing will continue to be quicker than it had been during the first half of Season 2.”

Of course, every series endures growing pains of one sort or another, and the tonal evolution between showrunners is hardly surprising. What’s been perhaps less predictable is the way the Walking Dead audience has continued to propagate with the kind of speed a zombie could hardly dream of. Executive producer Gale Anne Hurd admits that the original expectation was that the show would strictly appeal to a genre audience.

“No one expected that we would actually become part of the pop culture dialogue to the extent that we have,” Hurd acknowledges, “and I think it’s happened because the fans who enjoyed the show became our biggest proponents. I give credit to the cast bringing these complex characters to life — no pun intended. I also honestly believe there’s something to the zeitgeist, maybe because it’s 2012 and we have a feeling the apocalypse is right around the corner. It’s much less unsettling to imagine a zombie apocalypse than a real one.”

It was helpful during the tumult of the second-season transition to have Kirkman on-hand not only as an exec producer but “a fully integrated creative voice on our show,” Mazzara adds. ”He’s very mindful of the fan base and the comic book audience.” He notes that the show’s upcoming Season 3 storylines are what Kirkman refers to as “the good stuff” with the introduction of the Michonne character and the casting of David Morrissey to play the Governor.

But for all the success of Walking Dead, does Mazzara ever feel like those in the creative community still tend to dismiss it as a mere zombie show? “Maybe, and that’s OK,” he says. “And The Shield was just a cop show. You can reduce any show down to a simple sentence. But let ’em do it. That keeps us hungry and keeps us working hard.”

Hurd admits she does occasionally feel like “the poor stepchild” at AMC, considering its trio of more critically praised dramas. “We’re popular but we’re not very pretty,” she offers. “At the same time, it’s nice to be on a network that so stands for quality.”