Still, Mr. Medvedchuk has been close both politically and personally to Mr. Putin for more than two decades, and he was a prominent figure in the pro-Russian wing of Ukrainian politics, a circle where Mr. Manafort found several clients.
Mr. Putin is the godfather to Mr. Medvedchuk’s daughter. The two men met frequently over the years, and Russian air traffic control authorities granted special exemptions for Mr. Medvedchuk’s private jet on flights to Moscow, he said in an interview in 2017.
Some European politicians, including the former chancellor of Germany, Angela Merkel, had publicly endorsed a role for Mr. Medvedchuk as an intermediary in the standoff between Russia and Ukraine, given his personal ties to Mr. Putin.
But in Ukraine, outside of a narrow base of support mostly in the country’s east, he was widely viewed as a loathsome quisling who had reaped wealth from energy deals with the Kremlin while promoting Russian foreign policy goals, including weakening the central government under a federalization overhaul that he had championed for years.
At various times, he had served as deputy speaker of Parliament, a presidential adviser and a negotiator in prisoner exchanges with Russia. And as a figure at the nexus of various financial and political influence operations run by the Kremlin, Mr. Medvedchuk’s importance extended beyond Ukraine.
Mr. Manafort, before he became chairman of Donald J. Trump’s presidential campaign in 2016, worked for a decade as a consultant for Russian-leaning politicians in Ukraine, including the Opposition Bloc party, in which Mr. Medvedchuk was one of three leading figures.
Russia-Ukraine War: Key Developments
Mr. Manafort advised the party on its electoral strategy based on polling, Mr. Medvedchuk said in the interview in Kyiv in 2017. He recalled a party conference that the American consultant had attended ahead of parliamentary elections a few years earlier. Mr. Manafort, he said, had endorsed the party’s pro-Russia policies as electorally sound in Ukraine’s southeastern region.