Mark Strong (Sherlock Holmes) is playing Sinestro in Martin Campbell's upcoming Green Lantern based on the DC comics of the same name.  Sinestro is best known as the arch-nemesis of Green Lantern (who will be played by Ryan Reynolds), but the character was originally the Lantern's mentor and that's how we'll see him in the first film. Here's what Strong had to say about the character to USA Weekend:

Sinestro starts out as Hal Jordan's mentor, slightly suspicious and not sure of him because obviously Hal is the first human being who's made into a Green Lantern. He's certainly very strict and certainly unsure of the wisdom of Hal becoming a Green Lantern," Strong says. "He is a military guy but isn't immediately bad. It's the kind of person he is that lends himself to becoming bad over the course of the comics being written, but initially he's quite a heroic figure."

Hit the jump for details on how and why Strong is going to channel actor David Niven for his performance. Green Lantern is set to hit theaters on June 17, 2011.

Strong notes that the look of Sinestro was based off actor David Niven.  Says Strong:

"Obviously at the time, whoever was doing the original comics must have looked at them as guys doing very well in the film industry, and based those characters on them. So I would like to do justice to the Sinestro that was conceived for the comic books."

So what does that mean? Well, here's a clip of Niven from one of my favorite movies, The Guns of Navarone.  Niven won the Academy Award for Best Actor for his performance as Major Angus Pollock in the 1958 film Separate Ways.

Strong will next be seen in Kick-Ass and Robin Hood.  He's playing the villain in both films.