David Horowitz, the ex-radical firebrand who spent the last 40 years of his life exposing the left’s lies, hypocrisies, and crimes, died on April 29 after a long battle with cancer. He was 86.

A former Marxist intellectual and New Left insider who became one of the most prolific and pugilistic conservative writers of his time, Horowitz was many things: essayist, agitator, memoirist, mentor, and iconoclast. But above all, he was a political street fighter of the first order. He saw himself on a battlefield of ideas — and he had no interest in compromise.

Horowitz spent the second half of his life warning Americans about the first half. And he never, ever backed down.

He was also my first boss.

Born in Forest Hills, New York, in 1939 to Communist Party members, Horowitz was steeped in ideological certainty from the cradle. He earned degrees at Columbia and UC Berkeley, gravitated toward literary criticism, and helped lead the radical journal Ramparts in the 1960s. By the early ’70s, he was deep in the orbit of the Black Panthers, whose criminality and murder of Horowitz’s friend Betty Van Patter all but obliterated his faith in the left.

That trauma marked the turning point and the beginning of a long journey rightward. He completed his break from his old comrades in 1985, when he and his longtime friend and collaborator Peter Collier published a scorching essay in the Washington Post Magazine with the cheeky title “Lefties for Reagan.”

“One of the few saving graces of age is a deeper perspective on the passions of youth,” they wrote. “Looking back on the left’s revolutionary enthusiasms of the last 25 years, we have painfully learned what should have been obvious all along: that we live in an imperfect world that is bettered only with great difficulty and easily made worse — much worse. This is a conservative assessment, but on the basis of half a lifetime’s experience, it seems about right.”

Horowitz would later write in his autobiography that his “moral conscience could no longer be reconciled with the lies of the Left.” If it could kill and lie and justify it all in the name of justice, what the hell kind of justice was it?

Horowitz’s political evolution was more than a turn — it was a total break. And once broken, he threw himself into the cause of exposing the radicalism, corruption, and totalitarian impulses of his former comrades. He brought to the right a kind of inside knowledge and rhetorical ferocity that few others could match.

In the late 1980s, he and Collier (who died in 2019) launched the Center for the Study of Popular Culture — originally just a room in Horowitz’s house in the San Fernando Valley. “The name identified its focus,” Horowitz wrote, “but also made it harder for the Left to attack.” It wasn’t a think tank like Heritage or Cato. “Our combative temperament was hardly suited to policy analysis,” he admitted. The CSPC would become the David Horowitz Freedom Center in 1998 — what Horowitz proudly called a “battle tank.”

I started working there in 1994, fresh out of college. David and Peter gave me my first real job. I wasn’t there long — only a couple of years — but the lessons stuck. When I gave notice to join the Claremont Institute, Peter warned me: “I certainly wish you luck. I don’t think David will take the news very well, though.” Oh, boy, was he right.

“JESUS CHRIST! HOW CAN YOU DO THIS TO ME?” was David’s immediate, explosive reaction. Such outbursts were legendary in the office — others had gotten the same treatment — but after a talk, he settled down. I finished my two weeks, and he shook my hand and wished me well as I left.

It took me a while to understand his wild response. But as he admitted in “Radical Son,” he had “a strain of loyalty in me” and “an inability to let go of something I had committed myself to.” That loyalty was fierce. And once you were in David’s circle — whether as comrade or colleague — he expected you to stay. Nothing mattered but the cause. “I would not run when things got tough,” he wrote of his hesitation to break from the Panthers. It was personal for him, always.

Peter once described his friend to me as “four-fifths of a human being.” That was generous on some days. Horowitz could be cold, irascible, and prone to volcanic rage. But he also had a great heart, one which bore scars from a lifetime of tragedy and regret. One of his most affecting books is “A Cracking of the Heart,” the 2009 memoir of his rocky relationship with his daughter Sarah, a gifted writer in her own right, who died suddenly in 2008 at the age of 44. It’s the reflection of a fully formed human being.

I was proud to publish David’s work years later. It always tickled me when he pitched articles — my old boss, pitching me — but I was pleased to publish them out of gratitude for the start he and Peter gave me.

While David became famous for his political transformation, in some ways he never changed. “You can take the boy out of the left,” one wag quipped, “but you can’t take the left out of the boy.” Venture capitalist Ben Horowitz, David’s son, put it even more precisely: “While David became known for his change in views, in a sense he never changed at all.” His method of ideological engagement — fierce, unrelenting, totalizing, moralistic — remained constant. Once an ideologue, always an ideologue.

And thank God for that.

David launched and encouraged the careers of many others, including Donald Trump’s domestic adviser Stephen Miller and Turning Point USA founder Charlie Kirk. His Freedom Center helped shape the new generation of conservative activists — and sharpened the right’s sense of urgency and resolve. Though he often complained that Republicans lacked the stomach to fight, he lived long enough to see another political pugilist from Queens take and retake the Oval Office.

His nine-volume “The Black Book of the American Left” was arguably his life’s last great project, modeled in part on “The Black Book of Communism.” Where others flinched or equivocated, Horowitz named the threat. The left wasn’t simply wrong — it was dangerous, deceitful, and, at its root, totalitarian.

David Horowitz is survived by his wife, April, four children, and several grandchildren.

He spent the second half of his life warning Americans about the first half. And he never, ever backed down.

Editor’s note: A version of this article appeared originally at Chronicles Magazine.