(Reuters) - Clint Eastwood got the idea for his "very unorthodox" speech at the Republican convention hours ahead of time, and made a last-minute decision to cast an empty chair as an invisible President Barack Obama, the actor said in an interview with a California newspaper.

The "Dirty Harry" star told the Carmel Pine Cone in the interview published on Friday that he had little public speaking experience but felt his improvised chat with Obama had accomplished his goals. It was his first public comments about the unscripted speech he gave on Thursday last week.

Eastwood's remarks puzzled viewers and became the brunt of jokes.

"I may have irritated a lot of the lefties, but I was aiming for people in the middle," the Oscar-winning actor and director said in the interview. The newspaper serves the California town where Eastwood was mayor in the 1980s.

"They've got this crazy actor who's 82 years old up there in a suit," he said. "I was a mayor, and they're probably thinking I know how to give a speech, but even when I was mayor I never gave speeches. I gave talks."

Known for having some strong conservative opinions, Eastwood was quoted as saying that people who were shocked by his remarks "are obviously on the left."

For the full interview see http://www.pineconearchive.com/120907-1.html

Eastwood's conversation with an empty chair largely upstaged Republican presidential contender Mitt Romney's keynote speech at the convention and triggered a satirical Twitter account, @InvisibleObama, that went viral.

The @InvisibleObama parody account garnered more than 25,000 followers by the end of Romney's speech, and by last Friday afternoon it had some 55,000 followers.

The Twitter hashtag #eastwooding, mostly pictures of empty chairs, was one of the top-trending topics on the microblogging site last Friday.

Eastwood said he got the idea to use the chair while waiting backstage at the Tampa, Florida, convention arena.

"There was a stool there, and some fella kept asking me if I wanted to sit down," Eastwood said. "When I saw the stool sitting there, it gave me the idea. I'll just put the stool out there, and I'll talk to Mr. Obama and ask him why he didn't keep all of the promises he made to everybody."

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Eastwood told the newspaper that campaign aides for Romney had asked for details about what the actor would say to the convention. "They vet most of the people, but I told them, 'You can't do that with me, because I don't know what I'm going to say.'"

Eastwood said he had been invited by Romney to speak at the convention after endorsing the candidate in August. His speech was expected to last about 5 minutes but Eastwood spoke for almost 12 minutes.

The star of "The Good, the Bad and the Ugly" and "High Plains Drifter" was supposed to be a surprise speaker at the convention, but his name leaked out on the Internet as his appearance approached.

"It was supposed to be a contrast with all the scripted speeches because I'm Joe Citizen. I'm a movie maker, but I have the same feelings as the average guy out there," he said.

Eastwood said Romney went backstage to thank him and that he flew home the next day unaware of the headlines -- and controversy -- that his speech had triggered.

(Editing by Richard Chang)