Standing on the convention stage with an empty chair, Eastwood carried on a sometimes rambling conversation with an imaginary President Barack Obama. The Oscar-winning director of "Unforgiven" and "Million Dollar Baby" criticized Obama for failing to turn the economy around and for wanting to close the Guantanamo Bay prison for terror suspects.
"How do you handle the promises you've made? What do you say?" Eastwood asked the imaginary Obama. "I know even some of the people in your party were disappointed you didn't close Gitmo," the U.S. prison at Guantanamo Bay, Cuba.
"What do you mean 'shut up'?" said Eastwood, acting indignant. "I thought it was just because somebody had a stupid idea of trying terrorists in New York City."
At another point, the 82-year-old Eastwood acted as if he were listening to the imaginary Obama unleash a diatribe against Romney, poking Vice President Joe Biden and letting the convention audience guess what the president said.
"He can't do that to himself. You're absolutely crazy!" Eastwood responded. "You're getting as bad as Biden. Biden is the intellect in the Democratic Party. It's just kind of a grin with a body behind it."
The actor and director talked about Oprah Winfrey, the wars in Iraq and Afghanistan and lawyers. Eastwood said Obama has failed to deliver on his promises and it's time for Romney and his running mate, Paul Ryan, to take over.
At one point, Eastwood talked about the need for change.
"When somebody doesn't do the job, you gotta let 'em go," Eastwood said. The tough-guy actor of "Dirty Harry" fame drew a finger across his throat.
The crowd cheered Eastwood's entrance and shouted his famed catchphrase, "Go ahead, make my day." The freewheeling performance was a sharp contrast to the highly choreographed convention in which the Romney campaign has vetted the speeches.
Backstage, stern-faced Romney aides winced at times as Eastwood's remarks stretched on. The actor was the only speaker not reading from a teleprompter as he spoke. The machine was blank.
Twitter was instantly ablaze with comments mocking Eastwood's rambling speech.
Howard Kurtz, host of CNN's "Reliable Sources," tweeted that "Clint's empty chair act" was the "weirdest convention moment I have ever seen." Joe Scarborough, the conservative host of MSNBC's "Morning Joe," declared "a great night for Mitt Romney just got sidetracked by Clint Eastwood. Wow. That was bad."
Minutes after Eastwood began his speech, someone created the (at)InvisibleObama account on Twitter. It already has 17,000 followers and counting.
"Clint Eastwood is now backstage arguing with a vending machine," joked Canadian comedian Daryn Jones.
Film critic Roger Ebert didn't give the speech two thumbs up.
"Clint, my hero, is coming across as sad and pathetic," tweeted Ebert. "He didn't need to do this to himself. It's unworthy of him."
Comedian Roseanne Barr put it simply: "clint eastwood is CRAY."
Not everyone agreed.
"Clint Eastwood made my day," tweeted Southern rocker Charlie Daniels. The Hollywood trades gave it positive marks, perhaps a reflection of the movie world's appreciation for genuineness.
Eastwood endorsed Romney earlier this month at a campaign event in Sun Valley, Idaho.
Associated Press writers Kasie Hunt and Steve Peoples in Tampa, Fla., and Derrik J. Lang in Los Angeles contributed to this report.