Julius Maada Wonie Bio (born 12 May 1964) is a Sierra Leonean politician and former military officer who has served as the 5th president of Sierra Leone since 4 April 2018. He is a retired brigadier in the Sierra Leone Army and was the military head of state of Sierra Leone from 16 January 1996 to 29 March 1996, at only 32 years old in a military junta government known as the National Provisional Ruling Council (NPRC).

As military head of state, Bio returned Sierra Leone to a democratically elected government, when he handed power to Ahmad Tejan Kabbah of the Sierra Leone People's Party, following Kabbah's victory in the 1996 Sierra Leonean presidential election. Upon retiring from the military in 1996, Bio moved to the United States, where he was granted political asylum, and he did not visit Sierra Leone from the U.S. until 2005.

Bio ran as the Sierra Leone People's Party (SLPP) presidential candidate in the 2012 presidential election, but lost to incumbent President Ernest Bai Koroma. He ran again in 2018, defeating Samura Kamara of the ruling All People's Congress (APC).

As president, Bio has overturned most of the policies of Koroma, whom he accuses of corruption and mismanagement of the country's treasury. A deadly coup attempt to overthrow Bio failed in September 2023. Former president Koroma was detained and charged with treason as he was accused of being involved in the failed coup attempt.

Bio's government's handling of the economy was the target of a violent protest in August 2022. Bio was nevertheless re-elected the following year, though the elections were marred by violence and raised concern from international observers due to a lack of transparency in the counting process. As president, Bio has implemented free primary and secondary school public education and repealed the death penalty.

Julius Maada Wonie Bio was born on 12 May 1964, in Tihun, a village in the Sogbini Chiefdom, Bonthe District in the Southern Province of Sierra Leone. Bio was born three years after Sierra Leone's Independence during the administration of then Sierra Leone Prime Minister Sir Albert Margai of the SLPP. Bio is the 33 of 35 children born to Sherbro Paramount Chief Charlie Bio II of Sogbini Chiefdom. Bio's father had nine wives. Bio is named after his paternal grandfather Julius Maada Wonie Bio, who was also a Sherbro paramount chief of Sogbini Chiefdom. Bio is an ethnic Sherbro, and a practicing Roman Catholic.

Bio began his primary education at the Roman Catholic Primary School in Tihun, Bonthe District. After finishing his early years in primary school, Bio was sent to the town of Pujehun to live with his older sister Agnes, who was a primary school teacher in Pujehun. Bio completed his primary education at the Holy Family Primary School in Pujehun. After his primary education, Bio's older sister, Agnes, enrolled him at the Bo Government Secondary School in Bo (commonly known as Bo School), a prominent boarding school. Bio spent seven years at Bo School, rising to become school prefect. Bio graduated from Bo School in 1984 with A-level at age 20.

After graduating from secondary school, Bio applied for admission into Fourah Bay College in Freetown in 1985 at age 21. However, Bio ultimately enrolled in the Republic of Sierra Leone Armed Forces military academy at Benguema, just outside the capital city of Freetown. He trained as a cadet officer under the command of Major Fallah Sewa, the head of cadet training at the military academy.