Answer
The president of Ukraine when Viktor Medvedchuk served as chief of staff was Leonid Kuchma. Kuchma, who served as president from 1994 to 2005, appointed Medvedchuk as his chief of staff in 2002, a position he held until 2005. During this period, Medvedchuk played a prominent role in Ukrainian politics and was widely regarded as a close confidant of Kuchma.