【American classic porn movie Hot Lunch (1978)】

Robert Kirkman launched Invincible and The American classic porn movie Hot Lunch (1978)Walking Deadin the same year, but the former is set to end in 2017 while the latter shows no signs of slowing down.

The cynic's view of this divide is fairly straightforward: one is a beloved-but-not-blockbuster comic book series, the other is a transmedia phenomenon and cultural touchstone. One makes good money, the other makes all the money.

"I'm sure that's what people think, but ... it's certainly not that The Walking Deadis more popular," Kirkman told Mashableduring a New York Comic Con sitdown.

"The Walking Deadis more a story about the world to me. The characters are the most important aspects, but it's the characters within that world that drive the story."

Both stories have the formal structure of a beginning, middle and end. But that end isn't even in sight for The Walking Deadright now. It's really a question of scale.

"There's a much longer trajectory [in The Walking Dead] simply because telling a story about the crash and fall and evolution of society is a little bit more involved. I have a lot more to do on that one," Kirkman said.

"It's not a matter of running out of stories. It's just a different kind of story engine."

There was a time that Kirkman thought Invinciblewouldn't survive much more than a year. It's unthinkable now, after 13 years of stories about Mark Grayson and his Viltrumite heritage, but it's true.

"[Before Invincible] I had never really done anything that had lasted for very many issues," Kirkman said. "Around issue 8 or 9, I didn't know if there would be an issue 13. And then sales started going up and everything worked out."

That eventual success spurred Kirkman to think about the bigger picture of his trope-squashing superhero story. It's what led him to view the series -- as he mentioned in his "Invinciblewill end" announcement -- as a never-ending tale that could be passed down to future writers.

That thinking changed as he delved deeper into the series and fleshed out his cast of characters.

"I think there's a shift in the series if you're paying attention where things get a little bit more personal, a little bit more dramatic," Kirkman said. "It's not quite like 'There's a new villain every issue, he's fighting a new villain.'"

The comic's fans know this well.

Invinciblehasn't ever shied away from taking on real-world issues and concerns, covering everything from weight-shaming to rape to parenthood. Over-the-top comic book action is never far off, but it's framed against a familiar, frequently imperfect world.

Plenty of comics have covered similar ground, but not nearly as often in the realm of superhero stories.

"As much as I love Peter Parker as a character he doesn't really have a lot of character growth. There isn't really a story that is Spider-Man's story," Kirkman said.

"When Invincible ends you'll see ... that's what this book was about. It was about [Mark Grayson's] journey to being this person, and watching him grow from being a teenager to what he ends up being at the end of the book.

"I just got really excited about that and thought it would be a really cool thing to do."

The end of Invincibledoesn't necessarily mean the definitive end of that universe, but don't expect to see piles of spin-offs after Mark's journey ends. Kirkman admits that it's way too early for concrete plans -- the series isn't even over yet -- but he's open to the idea of coming back one day.

"I would never rule out coming back at some point to do something special," he said. "I like the idea of, maybe 10 years down the road, [current artist Ryan Ottley] and I getting back together with [original artist Cory Walker] and doing something that the three of us can craft.

"I mean, assuming everyone doesn't die in the last issue; you never know."