Russian authorities have detained outspoken pro-war blogger Igor Girkin, a hardline nationalist critic of Russia's flagging military campaign in Ukraine, also known as Strelkov.
His wife said he was taken away from their Moscow flat while she was not at home, and charged with extremism.
Strelkov, a former intelligence officer, played a key role in Russia's 2014 landgrab of Crimea.
He went on to lead Russia's proxy army in the ensuing war in eastern Ukraine.
He was one of three men convicted in absentia by a Dutch court last November of murder for his role in a missile strike in 2014 that downed a Malaysia Airlines passenger jet over the conflict area, with the loss of all 298 people on board.
But as the full-scale invasion of last year became increasingly bogged down, Strelkov's criticism of military failings and the commander in chief, President Vladimir Putin, became more vociferous.
"We have already lost," he told social media followers last year.
A few days ago he called the Kremlin leader "a nonentity" and "a cowardly waste of space", says BBC Russia editor Steve Rosenberg.
Strelkov's lawyer, Alexander Molokhov, confirmed he had been detained, but said it was unclear where and why he was being held.
The war-blogger has been allowed free rein to criticise the president and the military for a long time, so it is unclear what has led Russia's investigative committee to move at this point.
Opponents of Russia's so-called special military operation in Ukraine have been handed lengthy jail terms for far milder remarks.
But earlier this week a retired Russian intelligence officer, Vladimir Kvachkov, was charged with "discrediting" the Russian army. He and Strelkov had created the "Club of Angry Patriots", livestreaming their criticism of Russia's political and military leadership.
For many years, Strelkov, 53, had been considered untouchable, says BBC Russian's Ilya Barabanov.
That was partly because of previous role as colonel in the FSB Security Service, but also because he was identified as a suspect and later convicted of downing flight MH-17 while he was commander of Russia's proxy force in occupied Donetsk in eastern Ukraine.
Russian investigative website Agentstvo suggested that authorities had revised a previously unspoken rule allowing pro-war bloggers to vent their anger as much as they liked.
Commentator Tatiana Stanovaya said this was a moment that many among the siloviki - the president's inner circle - had eagerly awaited.
Strelkov had long ago "overstepped all conceivable boundaries", she said, but the failure of mercenary boss Yevgeny Prigozhin had left the army command with greater leverage to quash its opponents.
Prigozhin's Wagner group has had its powers dramatically cut since the botched mutiny last month, and the warlord himself has held back from his earlier expletive-laden tirades against the defence minister and army chief.
This week he appeared in a video, apparently filmed in Belarus, welcoming his fighters and saying that Russia's campaign in Ukraine was a "disgrace we want no part of".
Reports say that of the estimated 25,000 Wagner mercenaries, 10,000 are heading for Belarus while the others are going "on leave". One independent report said that Vladimir Putin had made a final decision that Wagner would cease to exist in Russia itself.