Despite the inflammatory rhetoric he instigates, Mr. Hannity is good-natured and humble in person, as interested in his children’s tennis matches as in Mitt Romney’s foreign policy positions. He rarely agrees to interviews, and when he did last week, he said he did not read negative articles about him, or even the friendly Twitter account all about his abundant head of hair. (A Fox hairdresser keeps tabs on the hair account for him.)

The son of a World War II veteran, Mr. Hannity delivered newspapers as a boy on Long Island, stirred controversy as a college radio broadcaster and then made his way to Atlanta radio in the early 1990s. He had been a guest on television, but not a host, when Mr. Ailes brought him to New York. “He saw something that I didn’t even think I knew I had,” Mr. Hannity recalled in an interview. “And he gave me the room to grow.”

The resulting show started on the same day as the Fox News Channel, Oct. 7, 1996, as “Hannity & Colmes,” with the mild-mannered liberal Alan Colmes cast as Mr. Hannity’s sparring partner. The debate fest began to routinely top CNN’s “Larry King Live” in the months after the Sept. 11, 2001, terrorist attacks, mirroring the rest of Fox’s ratings gains. About the same time, Mr. Hannity started a nationally syndicated radio show, capitalizing on his Fox fame. It is now No. 2 on radio, behind only Rush Limbaugh.

Mr. Hannity said he thought his “principled consistency” appealed to both listeners and viewers. In the park on Thursday night, Mr. Finley put it another way. “He has a good barometer for what the audience wants and what they expect,” he said, helped by radio listener calls.

After Mr. Obama’s election, Mr. Colmes left the 9 p.m. hour on Fox and it became Mr. Hannity’s alone, visibly moving the prime-time lineup further to the right. Mr. Hannity acknowledged that Mr. Obama might be perceived as good for his business, but quickly said, “What’s good for the country is more important than what’s good for Sean Hannity.”

Mr. Hannity’s hour has become something of a safe harbor for Republican challengers this year; one fan in the crowd Thursday, Aaron Johns, said he sensed that “when they’re on ‘Hannity,’ they’re more open” because “they’re not going to get tricked.” Still, Mr. Hannity recounted having to call Rick Perry “at least seven or eight times” to book him last month. “You’re killing me,” he said he told Mr. Perry. “The audience wants to see you. You gotta come on.”