MOSCOW — Before he was elected president of Ukraine last month, Volodymyr Zelensky played a president in a comedy show on television. The owner of that television station, Ihor Kolomoisky, returned on Thursday from self-imposed exile, raising fears that he may now ask the real president to return some favors.

Under the departing president, Petro O. Poroshenko, the Ukrainian government had nationalized a bank co-owned by Mr. Kolomoisky and accused him of siphoning off millions of dollars in fraudulent loans.

The Ukrainian government took over the bank, PrivatBank, in the course of a $5.6 billion bailout at a time when lending by the International Monetary Fund, the European Union and the United States was propping up the government.