- Defeated candidates Atiku Abubakar and Peter Obi are challenging his victory in court, alleging the result was manipulated.
- Mr Tinubu has rejected the allegation, and has hailed the peaceful transfer of power as "our enduring faith in representative government".
Bola Tinubu, 71, has been sworn in as Nigeria's president after winning the country's most competitive election since the end of military rule in 1999.
Widely credited with reshaping Nigeria's commercial hub Lagos, Mr Tinubu saw off a divided opposition party and a youth-backed third-party candidate in February's election.
Defeated candidates Atiku Abubakar and Peter Obi are challenging his victory in court, alleging the result was manipulated.
Mr Tinubu has rejected the allegation, and has hailed the peaceful transfer of power as "our enduring faith in representative government".
He has replaced Muhammadu Buhari, who has stepped down at the end of his two terms.
Africa's most populous country is facing a troubled economy, widespread insecurity and high inflation. Many will want Mr Tinubu to hit the ground running when he takes on one of Africa's most daunting jobs.
Once forced into exile by military ruler Sani Abacha, Mr Tinubu knows the value of freedom and wears it as an insignia on his signature hat - a broken shackle that looks like a horizontal figure of eight.
A trained accountant, it was the activities of the pro-democracy National Democratic Coalition (Nadeco) group, where he was a member, that brought him into Abacha's crosshairs.
The opposition of groups like Nadeco, and Abacha's death in 1998, ushered in Nigeria's democracy in 1999 and in many ways, Mr Tinubu, a former Mobil oil executive, feels entitled to Nigeria's presidency.
Mr Tinubu - known to his supporters as "Jagaban", which translates to "leader of warriors", a title from the Emir of Borgu in Niger state - will now be looking at unifying a country that is retreating into regional lines and religious blocs, as the election results showed.
But it is not a job that fazes him. He has pointed to his time as Lagos state governor between 1999 and 2007 to sell his candidacy to Nigerians.
Under his tenure, Lagos massively grew its income through huge foreign investment, while a public transport scheme that saw new lanes created for rapid buses eased the notorious traffic jams faced daily by commuters.
But the city of around 25 million people has not lived up to its reputation as a megacity despite his claims of turning it around.
Public infrastructure is largely in a state of disrepair - basic amenities such as water and public housing are decrepit, while a light rail project started during his tenure has not been completed almost 20 years later despite the riches of the state.
He has also been accused of keeping a grip on state finances despite leaving office in 2007.
Every governor that has succeeded him has been a protégé following a "grand roadmap", while one that dared to find his own path was quickly brought to heel, aided by powerful transport union members.
There are also allegations of corruption against Mr Tinubu, which he denies.
Two years ago, Dapo Apara, an accountant at Alpha-beta, a firm where Mr Tinubu purportedly holds stakes through a crony, accused him of using the firm for money laundering, fraud, tax evasion and other corrupt practices.
Mr Tinubu was sued despite him and Alpha-beta denying the allegations but all parties decided to settle out of court last June.
Such allegations, including twice facing Nigeria's Code of Conduct Tribunal (CCT), on allegations of breaching the code of public officers - where he was cleared - make opponents say Mr Tinubu is not the right man for the job in a country where corruption is high.
In the previous election, a brazen display of an armoured van used by banks to move money driving into his palatial compound in the Ikoyi area of Lagos fuelled suspicions that he was involved in vote-buying, which he made no great effort to deny.
"If I have money, if I like, I give it to the people free of charge, as long as [it's] not to buy votes," he said.
He is one of Nigeria's richest politicians but there are questions about his wealth.
In December, he told the BBC that he inherited some real estate which he then invested, but in the past he also said he became an "instant millionaire" while working as an auditor at Deloitte and Touche.
He said he had saved $1.8m (£1.5m) from his wages and other allowances, nearly the same amount found in accounts linked to him in a 1993 dispute with the US authorities.
In documents that are publicly available, the US Department of Justice alleged that from early 1988, accounts opened in the name of Bola Tinubu held the proceeds of sales of white heroin.
Kevin Moss, the special agent who investigated the operation, alleged that Mr Tinubu worked for their prime suspect Adegoboyega Akande.
While the court confirmed it had cause to believe the money in the bank accounts were the proceeds of drug trafficking, Mr Tinubu and the others denied the allegations, and the court never made a final order about the money's origins.
Instead, Mr Tinubu, who was not personally charged over the money, reached a compromise settlement with authorities and forfeited $460,000.
Mr Tinubu also faces questions about his health, once posting an eight-second video of him riding an exercise bike as proof of his fitness.
Opponents say his age is catching up with him and point to videos of various gaffes at campaign rallies where it can be hard to understand what he's saying.
Many Nigerians are wary of another president with health issues after President Umaru Yar'Adua died in office in 2010 and Mr Buhari spent considerable time getting medical treatment abroad.
But Mr Tinubu's supporters say he has the stamina for the job and is not competing for a spot at the Olympics.
During the campaign, there was some controversy about his choice of a running-mate.
Mr Tinubu, a southern Muslim, picked former Borno state governor Kashim Shettima, a northern Muslim, as his vice.
This move was seen as appeasing Nigeria's Muslim-majority north which has the largest voting bloc in the country.
However, it drew the ire of many Christians who say it went against the tradition of mixed-faith tickets for the presidency.
He defended his choice, saying he went for competence over primordial interests.
He is seen as the political "godfather" of the south-west region and its most influential figure, who decides how power is distributed among his many acolytes.
In 2015 he described himself as a "talent hunter" that puts "talents into office".
His immense political influence led to the merger of opposition parties in 2013 and eventually wrestled power from the then-ruling PDP in 2015 - a rarity in Nigeria where incumbents are not often defeated.
During his party primary, when it looked as though Mr Tinubu's aspirations were flagging, he reminded Nigerians that he was largely responsible for installing Mr Buhari after the former military ruler had failed on several occasions to win the presidency.
Mr Buhari's associates have since tried to downplay the former governor's influence in the 2015 election, but it is unlikely that Mr Buhari would have won, twice, without the backing of Mr Tinubu.
Having secured the presidency, Mr Tinubu will have to tackle many issues left behind by Mr Buhari - widespread insecurity, high unemployment, rising inflation and a country divided along ethnic lines.
It is not an impossible job, but the task ahead is daunting.