Many Nigerians are pinning their hopes on Nigeria's new president, Muhammadu Buhari, a former military ruler, who won a landslide victory on March 28 defeating President Goodluck Jonathan.

Abubakar Tafawa Balewa was elected chief minister of a coalition government in 1957, retaining the post as prime minister after independence in 1960. His government was troubled by regional factionalism. Nigeria has three dominant ethnic groups Hausa, Igbo and Yoruba. His work in furthering an indigenous African identity earned respect. He was killed in a military coup in January 1966.

A key figure in modern Nigerian nationalism, Nnamdi Azikiwe was the country's second and last governor general from 1960 to 1963. He became the first president of a federal republic of Nigeria, which was established in 1963. Azikiwe was ousted in 1966, leaving politics after another military coup some 17 years later. He died in May 1996.

Major General Johnson Aguiyi-Ironsi seized power in a military coup in January 1966 which led to the downfall of the First Republic. He suspended much of the constitution and sought to turn federal Nigeria into a single state. He was assassinated in yet another coup on July 29, 1966 after being office for just six months.

General Yakubu Gowon came to power in the military coup that toppled Aguiyi-Ironsi and ruled Nigeria from 1966 to 1975. In 1967, Biafra ceded from Nigeria triggering a civll war. The blockade imposed by Nigeria led to famine. Over a million civilians died from hunger and fighting. Biafran forces surrendered in January 1970. General Yakubu Gowon was himself ousted in a coup. He turned 80 in 2014.

General Murtala Ramat Muhammed ruled Nigeria from July 1975 to February 1976. He commanded the 2nd Division of the Nigerian Army during the Biafran War. After spending less than a year in power, he was killed in February 1976 when his car was ambushed in Lagos.

Major General Olusegun Obasanjo was the second-in-command to his predecessor Murtala Ramat Muhammed. Obasanjo governed Nigeria from 1976 until 1979 when he became the country's first military ruler to hand over power to a democratically elected civilian president, Shehu Shagari. Obasanjo was later a civilian president himself.

Alhaji Shehu Shagari (first from the left ) was the first and only president of Nigeria's Second Republic. Democratically elected in 1979, he campaigned under the banner 'One Nation, One Destiny." He faced allegations of corruption and electoral fraud and was succeeded by Major General Muhammadu Buhari after a coup. Shagari turned 90 in February 2015.

Major General Muhammadu Buhari was Nigeria's military ruler from December 1983 to August 1985. He is credited with fighting corruption and is remembered for his War Against Indiscipline. Critics accuse him of rights abuses. Buhari is the second military ruler after Olusegun Obasanjo to regain power in a civilian apacity. Like his predecessor, Buhari also lost power in a coup.

General Ibrahim Badamasi Babangida, or IBB, toppled Buhari in a bloodless coup and governed Nigeria from 1985 to 1993. Under his rule, a constitution for a Third Republic was drafted, but never enacted and presidential elections were held in June '93. MKO Abiola was the unofficial winner in a surprisingly free and fair poll. Banangida annulled the elections. He turned 73 in 2014.

Ernest Shonekan (center) was appointed interim president of Nigeria on August 26, 1993 by General Ibrahim Babangida who was under pressure to cede control of the country to a civilian government. Shonekan was in power for less than three months before he was toppled by his defense secretary, Sani Abacha.

Under General Sani Abacha (1993 to 1998) Nigeria saw strong economic growth, but also widespread rights abuses. Criticism grew more vocal after the hanging of Ogoni activist Ken Saro-Wiwa in 1995. After Abacha's death, Swiss authorities said almost all of the $500 million (457 million euros) linked to him in frozen bank accounts was 'obviously of criminal origin.'

General Abdulsalami Abubakar ruled Nigeria from June 1998 to May 1999. On taking office, he promised to hold elections within a year and transfer power to an elected president. To the surprise of some of his critics, he kept his word. Under his regime, Nigeria adopted a new constitution. This was the start of the Fourth Republic and military rule came to an end. In 2014, he turned 72.

Olusegun Obasanjo, a former military ruler, was elected president in a democratic poll in 1999. He was the candidate for the People's Democratic Party (PDP) and garnered almost 63 percent of the vote. He was reelected for a second term in 2003. He is credited with promoting Nigeria's prosperity and development. In 2015, he turned 78.

As the candidate for People's Democratic Party, Umaru Musa 'Yar Adua was elected president in 2007 in disputed polls which his rivals, Muhammadu Buhari (All Nigeria Peoples Party) and Atiku Abubakar (Action Congress) sought to have annulled. 'Yar Adua left Nigeria in November 2009, reportedly for medical treatment in Saudi Arabia. He returned in 2010 and died in May of that year.

Vice President Jonathan became acting president when 'Yar Adua left the country in 2009 and was sworn in as president on his death. Jonathan triumphed over Muhammadu Buhari in the 2011 election. He redeemed his uneven record as president by gracefully conceding defeat to Buhari in the 2015 poll, easing the way for an unprecedented peaceful transition of power from government to opposition.