Denis Sassou Nguesso (born 23 November 1943) is a Congolese politician and former military officer who has served as president of the Republic of the Congo since 1997. He also previously served as president from 1979 to 1992.

Sassou Nguesso headed the Congolese Party of Labour (PCT) for 12 years during his first period as president. His daughter Edith Lucie Bongo married Gabonese President Omar Bongo in 1989. He introduced multiparty politics in 1990, but was stripped of executive powers by the 1991 National Conference, remaining in office as a ceremonial head of state. He stood as a candidate in the 1992 presidential election but placed third.

Sassou Nguesso was an opposition leader for five years before returning to power during the Second Republic of the Congo Civil War, in which his rebel forces ousted President Pascal Lissouba. Following a transitional period, he won the 2002 presidential election, which involved low opposition participation. He was re-elected in the 2009 presidential election. That same year his daughter and her husband Omar Bongo died.

Sassou Nguesso passed a new constitution via referendum in 2015 amidst calls for boycott then a dismissal of results by opposition leaders. The new constitution enabled him to stand for another term. Sassou Nguesso was re-elected in the 2016 and 2021 presidential elections with a majority in the first round