Mr. Colmes conducts an interview in the “Spin Room” in 2004. (Chris Hondros/Getty Images)

Alan Colmes, a top-rated television and radio broadcaster who, as co-host with conservative Sean Hannity of “Hannity & Colmes,” became best known as the liberal in the “lion’s den” of Fox News, died at a hospital in Manhattan. He was 66.

His wife, Jocelyn Elise Crowley, said that he died late Feb. 22 or early Feb. 23 and that the cause was lymphoma.

Mr. Colmes joined the Fox News Channel on its founding in 1996, debuting with Hannity the evening the channel first went on air. “Hannity & Colmes” became the channel’s longest-running prime-time program — second only in the cable ratings to Fox News host Bill O’Reilly’s “The O’Reilly Factor” and outranking CNN’s “Larry King Live” — before Mr. Colmes left the show in 2008.

Facing off against Mr. Colmes, Hannity projected a style that invited comparisons to that of a bulldog. By contrast, Mr. Colmes, a onetime stand-up comic, was more peaceable — although no less convinced of his argument.

On his departure from “Hannity & Colmes,” he quipped that he was “proud that both Sean and I remained unharmed after sitting side by side, night after night for so many years.”

Reflecting on the odd couple they made, Robert Thompson, a Syracuse University scholar of television and popular culture, mused that “we’ve had perfect pairings of people who often don’t agree with each other — Siskel and Ebert come to mind. It always depended on bringing balance to that chemical equation.

“ ‘Hannity & Colmes’ was not one of those balances,” Thompson continued, recalling Hannity’s habit of frothing in the talk-radio tradition while Mr. Colmes attempted to proffer calmer arguments.

The Fox News viewership “enjoyed the mismatch,” Thompson said — the nightly tossing of Mr. Colmes “to the wolves.”

Mr. Colmes, a self-described liberal patriot, argued that he was at an inherent disadvantage on television, a venue that often favors oratorical aggression. Those who kept count noted that he often spoke fewer words per installment than Hannity.

“I don’t judge my effectiveness by how many words I say,” Mr. Colmes told The Washington Post in 2003. “I think liberals often see nuances in things. . . . Conservatives tend to see things in black and white. It gives them an air of certainty and conviction that might make them more comfortable to watch.”

Mr. Colmes gamely endured withering criticism from the left, which saw him as the Fox News token liberal. Some critics perceived betrayal in his presence on the channel, founded by Roger Ailes and Rupert Murdoch, to counterbalance what many conservatives view as left-wing bias in other news outlets.

Mr. Colmes’s loudest detractors included Al Franken, the comedian turned Democratic U.S. senator from Minnesota, who skewered Mr. Colmes in his book “Lies and the Lying Liars Who Tell Them: A Fair and Balanced Look at the Right” (2003). Franken derided Mr. Colmes as Hannity’s “liberal on-air punching bag” and “the lone Washington General,” a reference to the perennial losers to the Harlem Globetrotters.

“Some liberals have a problem with me simply because I work at Fox and nothing I do short of storming off the set in a rage will get them to respect that I work there,” he told Steve Young, an interviewer for the Huffington Post.

“I feel quite lucky to have the platforms I have on both television and radio,” Mr. Colmes continued. “Even if everything its detractors say about Fox were true, the most liberal of liberal attitudes would be that one would get credit for being in the lion’s den.”

After Mr. Colmes left “Hannity & Colmes,” Hannity continued hosting the show as a solo anchor. Mr. Colmes remained on air as host of “The Alan Colmes Show,” his radio program syndicated by Fox News, and as a Fox News commentator.

On the radio, the New York Times once noted, Mr. Colmes serenaded the listeners who wished him ill — and there was no shortage of them, he readily acknowledged — with recordings of tunes such as “Put a Little Love in Your Heart” and“I Can’t Make You Love Me.”

Alan Samuel Colmes, a grandson of Jewish immigrants from Eastern Europe, was born in Brooklyn on Sept. 24, 1950. His father, an auctioneer, ran jewelry stores with his mother. Mr. Colmes grew up in Lynbrook, N.Y., a Long Island community about five miles from the home town of Hannity, who was 11 years his junior.

Mr. Colmes was a 1971 speech graduate of Hofstra University on Long Island, where he began his radio career in high school as a DJ. He ventured into professional talk radio, broadcasting from Long Island, Boston and WNBC in New York, as well as taking occasional TV hosting gigs.

Hannity joined Fox at its inception and was slated to host a show akin to CNN’s “Crossfire.” Privately, the program was dubbed “Hannity & LTBD” — “Liberal to Be Determined.”

“Roger Ailes said to me, ‘You know any good liberals?’ ” Hannity told the Times. “So we started auditioning some.”

The “liberal to be determined” turned out to be Mr. Colmes, whom Hannity had debated on other television programming.

Mr. Colmes’s books included “Red, White and Liberal: How Left Is Right & Right Is Wrong” (2003) and “Thank the Liberals* *For Saving America (And Why You Should)” (2012).

Besides his wife of 13 years, who resides in New York City, his survivors include a sister.

Mr. Colmes confessed that, unlike Hannity, who sincerely hoped to persuade audiences of the rightness of his view, he saw limits in the power of their parrying.

“I don’t delude myself into thinking I’ll bring anyone around to my way of thinking, especially Sean Hannity,” Mr. Colmes told the Newark Star-Ledger in 2003. “The point of a show like this is to provide debate points, fodder and an entertaining exchange.”

He remarked that he enjoyed “having the other side around, if only to prove how right liberals are.”

“We’ll keep a couple of you libs around,” Hannity retorted in the same interview. “You’re fun.”

Adam Bernstein contributed to this report.