Question: Usman Mu'azu was the governor of Kaduna State during the reign of the military leader who became President of Nigeria in what year?

Context paragraphs:
Muhammadu Buhari: Muhammadu Buhari {'1': ", '2': ", '3': 'GCFR', '4': "} (born 17 December 1942) is the President of Nigeria, in office since 2015.  He is a retired major general in the Nigerian Army and previously served as the nation's head of state from 31 December 1983 to 27 August 1985, after taking power in a military "coup d'état".  The term Buharism is ascribed to the Buhari military government.

Hadiza Bala Usman: Hadiza Bala Usman (born January 2, 1976) is a Nigerian activist and politician.  She is currently the Managing Director of the Nigerian Ports Authority (NPA) as appointed by President Muhammadu Buhari on Monday 11 July 2016.  She was formerly the Chief of Staff for the Kaduna State Governor.  Bala Usman is an active member of the All Progressives Congress (APC).

Kaduna State University: Kaduna State University is in Kaduna, Kaduna State, Nigeria.  It was established in 2004.  It has seven faculties with over 39 departments.  The school library contains over 17,000 volumes of books.  It has two campuses: Kafanchan and Kaduna.

Nasir Ahmad el-Rufai: Mallam Nasir Ahmad El-Rufai (born 16 February 1960) is a Nigerian politician who is the incumbent Governor of Kaduna State and former Director General of The Bureau of Public Enterprises, the head privatisation agency in Nigeria and also the former Minister of the Federal Capital Territory, Abuja from 16 July 2003 to 29 May 2007.  He is a member of All Progressives Congress (APC) and elected as the Executive Governor of Kaduna State during the 2015 general elections in Nigeria.  His spell with the government began under the transition government of General Abdulsalami Abubakar, where he served as an adviser in the Transition government.  He was reportedly in self-exile during the tenure of President Umaru Yar'Adua.  In November 2009, Nasir EL-Rufai stated plans to come back home to Nigeria despite the high level of risk he will be under.

Kaduna: Kaduna is the state capital of Kaduna State in north-western Nigeria, on the Kaduna River, is a trade center and a major transportation hub for the surrounding agricultural areas with its rail and road junction.  The population of Kaduna was at 760,084 as of the 2006 Nigerian census.  Rapid urbanization over the past decade has created an increasingly large population, now estimated to be around 1.3 million.  Kaduna's name derives from the Hausa word "kada" for crocodile ("kaduna" being the plural form).

Religion in Kaduna State: Religion in Kaduna State mainly is Islam and Christianity.  The Sharia is valid for areas with a mainly Muslim population.  The Roman Catholic Diocese of Zaria, the Roman Catholic Diocese of Zaria, the Roman Catholic Archdiocese of Kaduna and the Roman Catholic Diocese of Kafanchan have their seat in the state.  An ecclesiastical province of Kaduna of the Church of Nigeria exists.  The Churches of Christ are present in the state.  Winners' Chapel, which has been founded by David Oyedepo, is a Megachurch in Kaduna City.  When the governor of Kaduna announced to introduce Sharia, violence in Kaduna City erupted.

Christianity in Kaduna State: Christianity is a very minority religion in Kaduna State in the Middle Belt of Nigeria.  The Roman Catholic Diocese of Zaria, the Roman Catholic Diocese of Zaria, the Roman Catholic Archdiocese of Kaduna and the Roman Catholic Diocese of Kafanchan have their seat in the state.  An ecclesiastical province of Kaduna of the Church of Nigeria exists.  The Churches of Christ are present in the state.  Christianity in Kaduna City includes Winners' Chapel, which has been founded by David Oyedepo, is a Megachurch.  Kaduna Stat has a conflict between Christians and Muslims; Sharia is valid in those parts of the State, which have a Muslim majority.  An Interfaith Mediation Centre exists.

Usman Mu'azu: Air Vice-Marshal (retired) Usman Mu'azu (1942–2008) was the military governor of Kaduna State, Nigeria from January 1984 to June 1988 during the military regime of General Muhammadu Buhari.

Alhaji Hassan Dalhat: Hassan Dalhat, (born December 31, 1936) at Kakaki quarters in the ancient city of Zaria.  He is a Nigerian seasoned bureaucrat and administrator who served at the upper echelon of the Kaduna state civil service.  He holds the traditional title of Cigarin Zazzau (The Conqueror) and District Head of Sabon Birnin Daji in Kaduna state.  The 3rd and last child of late Hajiya Fatima Dalhatu (1905-1998) and the 7th to late Alkali Dalhatu Muhammad (1885-1956).  His father was a respected and influential High Court Judge (Alkali) who had served at Anchau-Takalafiya and Makarfi in Kaduna state.  After the death of Alhaji Shehu Ladan (former GMD NNPC and first Cigarin Zazzau), the Emir of Zazzau, Alhaji (Dr) Shehu Idris honoured him with the prestigious title.  As District Head, he became a patron of both western and Islamic education as a means to succeed in modern Nigeria.  He is a people oriented leader who think less of himself and more of the less privileged.  After the death of his father in 1956, his elder brother Alkali Bashir Dalhatu became his guardian, while the late Maccido Dalhat CON (1932-2012) became his mentor, confidant and buffer.  Cigarin Zazzau is blessed with 3 wives and 10 children.

Mukhtar Ramalan Yero: Alhaji Mukhtar Ramalan Yero (born 1 May 1968) is a Nigerian politician who served as the Kaduna State Commissioner of Finance from 2007 till May 2010 when Patrick Ibrahim Yakowa named him as the Deputy Governor after he succeeded Namadi Sambo who became the Vice President of Nigeria.  In December 2012 he became Governor of Kaduna State after the death of Patrick Ibrahim Yakowa in a helicopter crash.

Supporting paragraphs: Usman Mu'azu Muhammadu Buhari
Answer: 2015