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The Incumbent and Winner: Goodluck Jonathan - Nigerian President Goodluck Jonathan cast his ballot in Otuoke. Jonathan, the incumbent and ruling party candidate, is often called an "accidental president," according to the Associated Press. The soft-spoken 53-year-old marine biologist became governor of Bayelsa state after the impeachment of its elected governor. Jonathan later became vice president under elected Muslim leader Umaru Yar'Adua after a widely criticized 2007 election. Yar'Adua left Nigeria for Saudi Arabia in late 2009. A power vacuum stalled the country for months until lawmakers voted to give Jonathan presidential powers in February 2010. Jonathan became president in May 2010 after Yar'Adua's death. Known for wearing the traditional caftan and bowler hat of his Niger Delta home, Jonathan is a Christian of the minority Ijaw ethnic group. (Photo: AP Photo/Godwin Omoigui)

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The Challenger: Muhammadu Buhari - Former military ruler Muhammadu Buhari first came to power in a 1983 coup. His regime executed drug dealers, returned looted state assets and sent soldiers to the streets with whips to enforce traffic laws. His "war against indiscipline" won many followers, though his regime detained journalists critical of the government and laws were passed allowing indefinite detention without trial, according to the Associated Press. Despite his recent assurances that he is a convert to multi-party democracy, some worry the perennial candidate could return to his autocratic ways. Still, the 69-year-old Muslim has drawn thousands to his rallies across Nigeria's dissatisfied North. (Photo: AP Photo/Sunday Alamba)

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The Challenger: Ibrahim Shekarau - Ibrahim Shekarau is a former teacher and educator who has served as the governor of Kano state in Nigeria's North. Under the 55-year-old’s administration his state saw officials stop giving polio vaccinations to the young over unfounded fears the vaccine was a Western plot to sterilize Muslims. (Photo: Courtesy of Ibrahim Shekarau)

Photo By Photo: Courtesy of Ibrahim Shekarau

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The Challenger: Nuhu Ribadu - Borrowing from President Obama's 2008 campaign slogan, Nuhu Ribadu based his platform on change. The former police official gained prominence in Nigeria after being appointed as the chairman of the Economic and Financial Crimes Commission by former President Olusegun Obasanjo. Ribadu, 50, pursued top politicians in the country, though critics say he targeted Obasanjo's opponents. Ribadu once estimated that corruption has cost Nigeria more than $380 billion since gaining its independence from Britain in 1960. After Yar'Adua came to power, officials reduced Ribadu's police rank. He fled the country in 2008 after what his lawyer described as a drive-by shooting. A Muslim from Adamawa state, Ribadu is the candidate of the Action Congress of Nigeria, the country's strongest opposition party, though his campaign has been plagued by missteps. (Photo: Courte...

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Map of Nigeria - Nigeria is twice the size of California, with an area of nearly 360,000 square miles. It is set on the Gulf of Guinea on the West African Coast and borders Benin, Cameroon, Chad and Niger. English is Nigeria's official language; more than 500 local languages and dialects are widely spoken. The main three language groups are Yoruba, Hausa and Ibo. Crude oil drives Nigeria's economy. However, about 80 percent of Nigerians live on $2 or less a day. (Photo: Wikipedia)

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Millions Vote - Up to 73.5 million Nigerians were eligible to vote on Saturday. Nigeria has an estimated population of 150 million people, making it Africa's most populous nation. It has more than 250 ethnic groups, which are split between a predominantly Christian south and Muslim north. A small percentage practices indigenous beliefs. Twelve northern states have implemented Shariah law, an Islamic code of conduct, though the government remains secular. In this image, women in Mashi line up to cast their votes. (Photo: AP Photo/Sunday Alamba)

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Counting of Ballots - Electoral officials count ballots in a classroom in Mashi. To win the election, the candidate needs a simple majority and 25 percent of the votes in two-thirds of the nation's 36 states.(Photo: AP Photo/Sunday Alamba)

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The World Watches - An international observer took notes at a polling place in Daura Saturday. (Photo: AP Photo/Sunday Alamba)

Photo By Photo: AP Photo/Sunday Alamba

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Proof of Vote - An election official inked the finger of a voter at a polling place in Daura to show that she has voted. Though Jonathan is expected to win, he said Saturday that he would not interfere with the electoral process. "I pray I don't go into a by-election because of the cost implications," Jonathan said. "We pray that whoever will win, will win."(Photo: AP Photo/Sunday Alamba)

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Underage Voting - Despite not being eligible to vote, an underage voter waits as an election official finds his name on a registry in the village of Doge Game. The minimum voting age in Nigeria is 18.(Photo: AP Photo/Jon Gambrell)

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Hotel Bombed - Hours after polls closed a bomb was detonated at a hotel in Kaduna in northern Nigeria, wounding eight people. (AP Photo/Sunday Alamba)

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Legislative Elections - Legislative elections earlier this month left a hotel ablaze, a politician dead and a polling station and a vote-counting center bombed. The day after the legislative elections, a vendor holds up a local newspaper with the headline Blood and Bombs on April 10. A coalition of local observer groups say Nigeria's first of three important April elections was ''not perfect'' but it offered an improvement over past flawed polls. (Photo: AP Photo/Sunday Alamba)

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President Goodluck Jonathan, a Christian who came to power after the death of the country's elected Muslim leader in May 2010, was the front-runner heading into Saturday's election. In this image, supporters of the ruling party, with painted faces and clothes in the colors of the party, wait for the arrival of Jonathan for the final campaign rally ahead of presidential elections, in Abuja last month. (Photo: AP Photo/Sunday Alamba)