UPDATED: One day after the show's Comic-Con panel, The CW comic-book drama names its big bad, with executive producer Marc Guggenheim saying, "We didn't want to over-milk it."

One day after its own Comic-Con panel, Arrow has unveiled its main villain for season three.

Oliver Queen and Co. will be up against one of the most prolific DC villains: Ra's al Ghul. The big surprise was revealed Saturday evening after an extended season-three trailer debuted during DC Entertainment/Warner Bros. TV's three-hour extravaganza, hosted by Arrow's own Stephen Amell, in the cavernous Hall H. For the team behind Arrow, getting Ra's al Ghul to appear in the Starling City universe was in the works for awhile.

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"It really happened very organically in the sense that we had this notion that in episode 16 we were going to reveal that Malcolm Merlyn was trained by the League of Assassins and that's because that's because of the comic book. We were like, you know what we're going to do? We're going to get away with a little reference about a guy in Nanda Parbat who changed his life," executive producer Marc Guggenheim tells a handful of reporters Saturday. "That was just the beginning."

It was the season-two episode, "Broken Dolls," where producers thought to start dropping in Easter eggs for Ra's al Ghul. "We just slowly started creeping towards it and creeping towards it. Then discussions started happening with DC and then Superman-Batman started getting into clearer focus," he said. "The character seemed to be available as far as not being used in the movies. It was a very, very organic progression. That was what was fun for us, just how natural it happened."

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As Guggenheim tells it, Arrow's version of Ra's al Ghul will be distinctive enough. "We have a really clever way of doing Ra's this year that is true to the comic-book origins but different from the way Ra's was portrayed in the Nolan movies. You don't want to compete with Batman Begins, even though we've always said Batman Begins was a big influence on us," he says. "We really wanted our Ra's to be very different — at least our own Arrow-ified version."

There was a lot of thought given to how much to dole out the Ra's al Ghul name during Arrow. "When we were talking about Ra's in the third episode in season two, it was [a question of] how many times should we mention his name? How often should we talk about him? Because he has a lot of power especially on the comic-book side. We didn't want to over-milk it and overuse it," Guggenheim says.

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"We not only show you a little hint of Ra's, we also repeat all the times we mention his name, which shows you how long we've been talking about this and thinking about this," he continues.

During the session, executive producer Andrew Kreisberg revealed that there may be a chance Merlyn and Oliver could team up, now that there's a common enemy. "We've established firmly that Ra's al Ghul hates Merlyn and Oliver doesn't like Merlyn," he said on the Hall H stage. "It's going to be series of who hates who more. The enemy of my enemy is my friend." Though the theme of Arrow remains "identity," Kreisberg added that "allegiance and loyalty" were also part of the season's arc. "What side are you going to take?"

Casting is underway for Ra's al Ghul, who will appear early in the third season though Guggenheim remained mum on when.

There's already history for Ra's al Ghul, who has been mentioned by name over the course of the past two seasons as a distant, but powerful overarching villain. His daughter, League of Assassins member Nyssa al Ghul (Spartacus' Katrina Law), was the first from the family to appear on Arrow, though other characters such as Sara Lance (Caity Lotz) have had League ties. Nyssa "will absolutely play into the season and we have a really cool arc planned," Guggenheim says. "The first time we see Ra's is a scene between him and Nyssa."

Ra's al Ghul has been prominently featured in the media, most recently in Christopher Nolan's Batman films Batman Begins and The Dark Knight Rises with Liam Neeson as the portrayer.

Another new character heading to Arrow in the new season will be Wildcat, who will have an encounter with Laurel (Katie Cassidy).

Email: Philiana.Ng@THR.com

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