Not unexpected, but stunning nevertheless: Washington Post executive editor Marty Baron is retiring after eight years at the helm, according to Brian Stelter of CNN. Baron was widely regarded as the best newspaper editor of his generation, and his leadership — not just at the Post but as a voice for journalism and the First Amendment — will be hugely missed.

Under Baron, the Post was fearless, negotiating the bizarre media landscape dominated by Donald Trump with a sure-footedness that its larger competitor, The New York Times, never quite seemed to master. Before coming to the Post, Baron was the editor of The Boston Globe, where he led the paper's reporting that showed Cardinal Bernard Law was deeply involved in the pedophile-priest crisis.

I interviewed Baron several times over the years, including in early 2016 for my book "The Return of the Moguls: How Jeff Bezos and John Henry Are Remaking Newspapers for the Twenty-First Century." Here is an excerpt about Baron's reaction when he learned in August 2013 that Amazon founder Jeff Bezos was buying the Post:

"I was completely shocked, obviously," Baron said when I asked him about his reaction to the news that Bezos would buy the Post. "I told people when I came here that while the Times would probably like to sell the Globe, it was highly unlikely that Don Graham would be selling the Washington Post. So I was kind of stunned when I heard about it. But I thought that it could have some real advantages for us"—a reference to Bezos's preference for growth over cutting and his deep understanding of technology and consumer behavior. "I did not know if it would be a good thing for me personally," Baron added, "because obviously when a new owner comes in he has the absolute right to pick who he wants to run the organization that he has acquired. He said positive things at the beginning, but my sense was that it would be a year of figuring out the place and deciding what he wanted to do."

Bezos, to his credit, realized what he had inherited, kept Baron in place and by all accounts left him alone to do his job. The Post has built its paid digital subscription base from around 100,000 to 200,000 in early 2016 to 3 million today, and the newsroom has grown from 580 to more than 1,000 since Bezos bought the paper. It's also been profitable for five years.

And the Post's main selling point has been the excellence of its journalism. Baron is going to be incredibly difficult to replace.