Who is Nigeria's Muhammadu Buhari?

 (CNN)Muhammadu Buhari has ruled Nigeria before, as one of a line of military strongmen who dominated the country between 1966 and 1999.

A military coup brought Buhari to power in late 1983 -- closing a brief period of popular rule by Shehu Shagari -- and another military coup ousted him from power in August 1985.

Buhari's 20-month rule was known for what he described as a "war on indiscipline," a tough regime which some say was marred by human rights abuses.

The 72-year-old retired major general's experience as a military ruler has been viewed as a plus by some and a minus by others in present-day Nigeria, where the government has been locked in a deadly battle with the militant group Boko Haram.

Nigerian economy weighs on voters' minds 02:54

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This year alone, the extremists have killed at least 1,000 civilians, Human Rights Watch says. The ongoing violence in the Northeast has put security -- along with corruption and the economy -- at the top of the election agenda.

Ayo Johnson, a documentary filmmaker and analyst on African affairs, told CNN earlier this month that the elections would come down to who could make Nigeria feel safe.

"Many Nigerians will not forget (Buhari) was a military leader, during a dictatorship," Johnson said. "Or maybe they will feel that they need a military leader to address fundamental problems such as terrorism."

Buhari has campaigned as a born-again democrat to allay fears about his strict military regime, while stressing that Nigeria's security needs to be the next government's focus.

"It's a question of security. Whether I was a former military officer or a politician through and through, when there is insecurity of this scale in the country, that takes the priority," he said from his campaign plane.

'Judged harshly'

In an interview with CNN's Christiane Amanpour in February, Buhari blamed President Goodluck Jonathan's government for repeated setbacks in the fight against extremists.

Buhari speaks to CNN's Amanpour08:52

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"The misappropriation of resources provided by the government for weapons means the Nigerian military is unable to beat Boko Haram," he said.

Asked by Amanpour about abuses allegedly committed during his own previous leadership, Buhari said there was "a degree of accuracy" in the claims.

But he said he had ruled Nigeria as part of a military administration.

"When that military administration came under my leadership, we suspended -- as a military then -- part of that constitution that we felt would be difficult for us to operate and as also a consensus," he said. "I think I'm being judged harshly as an individual that what happened during a military administration can be extended under a multiparty democratic system."

Buhari's campaign was also fiercely anti-corruption. He ran under the slogan of "new broom," and his supporters were often pictured holding brooms in the lead-up to the vote.