Who Is Sidney Blumenthal, Hillary Clinton's Outspoken, Unfiltered Confidant, Who Described John Boehner As A "Louche Alcoholic"?

On Monday night, the State Department released its latest batch of declassified Hillary Clinton emails, but the most revealing and provocative messages were not from her. Among the 7,000-plus pages stood out a longtime Clinton family confidant, who spoke candidly on just about every subject, from Iran to John Boehner. Though he was often unfiltered, he was also often astute in his political analysis, and as the emails show, Clinton regularly relied on his advice. Now, as the public continues to follow Clinton's email saga, it's wondering just who is Sidney Blumenthal, Clinton's free-speaking confidant?

As Secretary of State, Clinton often worked with intelligence agencies and foreign policy experts to gather information and make decisions, but perhaps nobody covered more ground or offered such forthright insight than Blumenthal. He was a veritable one-man news agency feeding Clinton information out of Libya, Saudi Arabia, Israel, Northern Ireland, China, Greece, and virtually everywhere else in the world. Along with hard data like election polls and news articles, Blumenthal also offered his personal take on how she should handle certain situations. For example?

When it comes to Iran, "harsh, targeted sanctions are absolutely necessary, but are most effective diplomatically when always coupled with an offer to negotiate." In other words, "the iron fist in the velvet glove approach."

As for Israel, "Without 'tough love,' any support for Israel will lack credibility."

JAMAL A. WILSON/AFP/Getty Images

He also didn't mince words about the Republican party:

The political discussion must be shaped and shifted; and the GOP must be put on the defensive and begin to pay the price. ... The Republican Party today is a captive party. It is captive to the swamp fevers of the extreme right.

And one Republican in particular?

Boehner is despised by the younger, more conservative members of the House Republican Conference. They are repelled by his personal behavior. He is louche, alcoholic, lazy, and without any commitment to any principle.

Yeah, but how do you really feel, Blumenthal?

So just who is Blumenthal and what makes him so qualified to offer Clinton such broad yet specific — and unfiltered — insight? Besides being a political adviser, Blumenthal is an established journalist with a focus on politics and foreign policy. He has served as editor and contributed to renowned publications such as The Washington Post, The New Yorker, and Vanity Fair. He has also authored several books, including a series of essays criticizing George W. Bush's presidency titled How Bush Rules: Chronicles of a Radical Regime and a pro-Clinton memoir titled The Clinton Wars.

Blumenthal became close with the Clintons when he served as a top aide to President Bill Clinton from August 1997 to January 2001, advising him on communications and public policy. During his advising Bill, Blumenthal established a loyalty to the Clintons that would carry over into Hillary's tenure as Secretary of State.

Regardless of how closely Hillary follows his political advice, it's clear that she is keen on hearing it. In one reply to Blumenthal, Hillary wrote, "Keep 'em coming when you can."