It’s somehow fitting that Alan Colmes got his start in standup comedy, since he needed a strong sense of humor—and equally strong debating skills—to spar with Sean Hannity and other conservatives at Fox News.

The unabashedly liberal commentator, who died this morning at 66 after a brief illness that has not been disclosed, gained national fame as one-half of the “Hannity & Colmes” show that launched when FNC did in 1996. But his roots were in radio, working for such powerhouse stations as WABC and WNBC in New York. Colmes remained a Fox News contributor and Fox radio host after the channel ended the prime-time partnership and made Hannity the solo host just before the start of the Obama administration.

Colmes faced a difficult challenge in his heyday as Fox’s most prominent left-wing voice, doing battle not just with Hannity but with Bill O’Reilly and other hosts. His views were not popular with much of the Fox audience, but liberals sometimes criticized him for not being more forceful against Hannity.

The reason the duo’s chemistry worked, even as their clashes sometimes turned contentious, is that Colmes leavened his arguments with wit, often flashing a broad grin. “I take some great pride in seeing how I’ve aged you over the years,” he told Hannity on air.

In a statement, Hannity said: “Despite major political differences, we forged a deep friendship. Alan, in the midst of great sickness and illness, showed the single greatest amount of courage I’ve ever seen. And through it all, he showed his incredible wit and humor that was Alan’s signature throughout his entire life. I’m truly heartbroken at the loss of a dear friend.”

Despite his uber-liberal image, Colmes once told USA Today: “I'm quite moderate ... I follow [Rush] Limbaugh on about 100 stations and I precede other conservatives, so I may be the only person giving a different point of view.”

But there was no mistaking what side he was on, as was clear when he published his 2003 book “Red, White & Liberal: How Left is Right and Right is Wrong.”

When his 12-year run in Fox’s prime-time lineup ended, Colmes said in a statement that he had approached management about taking on new challenges. “Although it’s bittersweet to leave one of the longest marriages on cable news, I’m proud that both Sean and I remained unharmed after sitting side by side, night after night for so many years,” he said.

Colmes is survived by his wife Jocelyn Crowley, a professor of public policy at Rutgers University. The family, which asked for privacy, said in a statement: “He was a great guy, brilliant, hysterical, and moral. He was fiercely loyal, and the only thing he loved more than his work was his life with Jocelyn.”

In an era of political polarization, perhaps his most enduring trait was that even those who fiercely disagreed with him found Alan Colmes likable.