I think that, for the most part, Ukrainian oligarchs put him there. It was his predecessor, Poroshenko, who the US had installed.

Daily Beast, 2019: Billionaire Ukrainian Oligarch Ihor Kolomoisky Under Investigation by FBI

Brunson pointed to Kolomoisky’s role in funding the ultra-far-right Azov battalion, a group of Ukrainian fighters alleged to have ties to American white supremacists, per RFE/RL; the State Department has called its political wing a “nationalist hate group,” and human rights workers say it may be a haven for neo-Nazis.

Kolomoisky has a host of enemies. He’s been accused of commissioning contract killings. And in 2016, Ukraine’s central bank nationalized Kolomoisky’s PrivatBank because it didn’t have enough cash. Billions of dollars disappeared from its coffers because it lent so much to Kolomoisky associates, according to the FT. The move was widely viewed in the West as a victory for transparency and good governance, in a country whose politics are impoverished on both counts. It was a flashpoint in Kolomoisky’s relationship with Poroshenko, and many speculate the oligarch backs Zelensky in part because hopes to depose the president who oversaw the takeover of his bank.

CNN, 2023: Ukrainian oligarch and Zelensky supporter Ihor Kolomoisky arrested in fraud investigation