Vladimir Putin marked what was essentially 20 years as head of Russia’s government on New Year’s Eve. Since becoming acting president after Boris Yeltsin’s resignation on Dec. 31, 1999, Putin has increasingly tightened his grip in power. This month, he shook up the Russian governmentin a move some say laid the groundwork for extending his grip on powerbeyond the end of his term in 2024.

So far, one person has become a major thorn in Putin’s side. He is Mikhail Khodorkovsky, at one time one of Russia’s seven oligarchs and an ally of Putin, and now an enemy who served 10 years in prison and is wanted for murder in Russia. Now based in London, he has become a major force in Russia’s pro-democracy movement.

Alex Gibney’s “Citizen K,” opening in theaters Friday, Jan. 24, is essential viewing for anyone needing a history lesson about Russia since the fall of the Soviet Union, and who wants a frontline report on the current geopolitical landscape in Europe, including Ukraine.

And yet one person this movie is not about, in case you were wondering, is President Trump. There is a brief, one-sentence allusion to Russian interference in the 2016 U.S. presidential election, but that’s it. Any inferences you draw between Putin’s rise and methods and Trump’s story might or might not have been intended.

Instead, this is a painful portrait of unfettered capitalism, when in the vacuum of the collapse of communism seven men took advantage of a period of chaos and emerged owning 50% of Russia’s wealth. Khodorkovsky started Russia’s first privately owned bank and later controlled the country’s largest oil company.

In the course of this, there were, likely,shady dealings. In the 1990s, Moscow was the murder capital of Europe. Khodorkovsky and the other oligarchs had private security details that were more like small combat army units.

“Your wild, wild West lasted decades,” Khodorkovsky says to the Americanfilmmaker Gibney. “Ours lasted only seven years.”

Law and order was restored thanks to a corrupt understanding between the oligarchs and Boris Yeltsin, the first president of the Russian Federation, and later Putin. This was meant to be only a stopgap, though — according to Khodorkovsky and Gibney — to get the government back on its feet and prevent a relapse into totalitarianism.

Putin used the situation as an opportunity to further strengthen his own power, and by the early 2000s all of the oligarchs either fled Russia or were arrested, as was Khodorkovsky.

Gibney (“Enron: The Smartest Guys in the Room”), who last trained his eye on the Theranos scandal in last year’s “The Inventor: Out for Blood in Silicon Valley,” paces “Citizen K” like a globetrotting John Le Carre thriller. One can quibble about whether he went too easy on Khodorkovsky, who really might be guilty of murder, but he does ask enough tough questions and Khodorkovsky is forthright enough, if intentionally vague, about his past misdeeds.

Khodorkovsky served 10 years in prison and all of his companies were taken over by Putin, but he was crafty enough to stash about $400 million in offshore reserves that help fund his current altruistic pursuits. He might be reformed, but he’s no angel.

And that’s a strength in this documentary. It becomes clear that it will take a strongman to bring down a strongman, at least in this case.

N“Citizen K”:Documentary. With Mikhail Khodorkovsky. Directed by Alex Gibney. (Not rated. 126 minutes.)