Oleksandr Muzychko, a prominent member of Ukraine's controversial Right Sector movement, was shot dead overnight in the western Ukrainian city of Rivne.
Muzychko, a burly, volatile man with a violent temper, was one of the most recognizable members of the far-right, nationalist grouping.
A series of videos posted on social media during the Euromaidan protests showed Muzychko, 51, alternately slapping a local prosecutor
and threatening lawmakers
with a Kalashnikov rifle as he demanded compensation for slain demonstrators.
At a time when many Euromaidan organizers were desperate to keep the protest movement peaceful, Muzychko and other Right Sector members, operating under leader Dmytro Yarosh, were committed to a militarized fight against the regime of now-ousted President Viktor Yanukovych.
"The person who holds the Kalashnikov is the person who calls the shots," Muzychko was quoted as saying.
WATCH: Oleksandr Muzychko Slaps A Prosecutor
WATCH: Muzychko Threatens Lawmakers With A Kalashnikov
Speaking to RFE/RL's Ukrainian Service just over a week before his death, Muzychko spoke angrily about the government's failure to prevent Russia's annexation of Crimea.
"The authorities should have ordered mobilization and put the military on high alert a long time ago because our country is being occupied now," he said. "Foreign troops are occupying parts of our country. They have occupied Crimea and are provoking our troops. Special [foreign] military units and saboteurs are operating throughout Crimea."
WATCH: Muzychko Speaks To RFE/RL's Ukrainian Service
Muzychko, who also went by the name "Sashko Biliy," was a frequent target of Russian authorities looking to portray Euromaidan protesters as neo-Nazis and fascists eager to kill Russians and Jews.
He had enemies both inside and outside Ukraine. At the time of his death, he was under investigation by a Ukrainian organized-crime unit.
He was also the object of an international arrest warrant, issued this month by Russia, for allegedly torturing and killing some 20 Russian federal military personnel during the war against Chechen separatists in 1994 and 1995.
Right Sector, and particularly its leader Yarosh, had sought to parlay their role in the overthrow of the Viktor Yanukovych government into political authority.
But the interim government failed to strike a deal with Yarosh on a security post, fueling speculation that Yarosh -- or, according to the Russian media, even Muzychko himself -- would run for president in the country's May elections.
With contributions from RFE/RL's Ukrainian Service