Final answer:
Mikhail Gorbachev was a reformist Soviet leader who initiated perestroika and glasnost, but his policies inadvertently led to the dissolution of the Soviet Union after an unsuccessful coup attempted by conservative party members.
Step-by-step explanation:
The term that best describes Mikhail Gorbachev during his tenure as the leader of the Soviet Union is that of a reformist. Gorbachev recognized the critical state of the Soviet economy and the public's desire for change. In response, he initiated policies of perestroika and glasnost. Perestroika, meaning 'restructuring', aimed to revitalize the Soviet economy through the introduction of semi-capitalistic, market-like reforms within the socialist system. This was complemented by glasnost, meaning 'openness', which allowed for increased transparency and freedoms in the government, including the freedom to criticize it. These reforms, although intended to save the Soviet Union, led to its eventual dissolution as they spurred demands for greater autonomy and independence from the Soviet republics.
Despite his efforts to keep the Soviet Union together, conservative factions within the Communist Party were dissatisfied with the direction Gorbachev was taking. This culminated in an attempted coup in August 1991. However, the coup was thwarted with the aid of Boris Yeltsin, the leader of the Russian republic, who would later succeed in dissolving the Soviet Union in December 1991 in coordination with other Soviet state leaders.