The movie will feature an extensive flashback on the past of Jackson's character, Jasper Hale, who became a vampire during the Civil War.
"It was just really fantastic to get to delve in there and to get to don all the Civil War regalia and whatnot. That was a pleasure," Jackson told MTV News. "I had to wear this wool suit of a major, cavalry major. I got the big hat and everything. Hop off the horse, bow to these ladies, and then I get eaten. And then I get turned!"
And the star's big role features a bunch of stunts – and time as a "bad dude."
"I got to go back into my old roots, got to ride some horses again, which was nice. Got to put these riding boots to use, which is good," he said, explaining, "I actually can ride a horse."
The actor, who had fight training from his role in "The Last Airbender," was also able to put his work in hand-to-hand combat and weapon fighting to use in "Eclipse."
"[Jasper was a] bad vampire," Jackson said of his character's beginnings as a trainer of newborn vampires – knowledge he must use to help the Cullens prepare to fend off Victoria's (Bryce Dallas Howard) newborn vampire army.
However, the dangerous role had one silver lining – it gave him the chance to share the screen with Bella (Kristen Stewart).
"It's actually the first time Bella and Jasper interact that's longer than one sentence, or me attacking her," Jackson laughed. "Kristen and I kept saying it was really nice to get to work together because we had never had a chance to really, kind of, like, get into some dialogue."
"Eclipse" is due in theaters in May 2010, with "New Moon" arriving on November 20.
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