Roger E. Ailes, who shaped the images that helped elect three Republican presidents and then became a dominant, often-intimidating force in American conservative politics at the helm of Fox News until he was forced out last year in a sexual harassment scandal, died on Thursday morning. He was 77.

The cause was complications of a subdural hematoma that Mr. Ailes sustained when he fell and struck his head on May 10 at his home in Palm Beach, Fla., the local authorities said.

“Fair and balanced” was Mr. Ailes’s defining phrase for Fox News, along with another slogan: “We report. You decide.” Though routinely mocked by liberal critics, who regarded the network as decidedly unfair and imbalanced, those words amounted to an article of faith for Mr. Ailes, who created Fox News with Rupert Murdoch’s money and guided it for two decades.

“If we look conservative,” he said, “it’s because the other guys are so far to the left.” In his mordant humor, CNN stood for Clinton News Network and CBS for Communist Broadcasting System. What Fox News did, he said, was apply a necessary corrective.