John Magufuli was the fifth president of Tanzania since its independence in 1961.
He was elected president for the first time in October 2015, with 58% of the vote and succeeded Jakaya Kikwete - enjoying a high approval rating.
His party, the Chama cha Mapinduzi (CCM), which has been in power since the country's independence, chose him to represent it among more than thirty candidates.
Before becoming president, John Magufuli, who comes from a modest family and holds a degree in chemistry, was a minister several times from the early 2000s.
He was entrusted with the portfolios of livestock and fisheries, housing and public works.
His resolute action in favour of housing for the poorest had already earned him the nickname of "Tingatinga", the Bulldozer in Swahili, in reference to the construction programmes he implemented.
He stands out for his resolute action in favour of the poorest. He wanted to demonstrate this form of empathy as soon as he was invested, taking a whole series of drastic measures.
In particular, the sums that previously evaporated in tax fraud will be invested in education and the fight against poverty.
As head of state, he promised to fight corruption, develop the country and its economy and launch major works.
As soon as he was elected, he divided his own salary by four, making him one of the lowest-paid African heads of state, cut public spending drastically, cancelled independence ceremonies as too costly, and began sweeping the streets of the capital, Dar es Salaam, himself to set an example.
Elected on the promise to put an end to corruption, he also put pressure on the big companies present in the country to force them to let the Tanzanian state take a stake in their capital, renegotiated the contracts of certain mining and gas companies, and dismissed local executives deemed corrupt or incompetent.
No area seems to escape presidential vigilance: to put an end to badly parked vehicles in the capital, it is decided that the police will confiscate their tyres.
John Magufuli was re-elected last October, in a contested election, with more than 84% of the votes.
According to the Tanzanian constitution, Ms Hassan will become the country's first female president and will consult with the ruling CCM party on the appointment of a new vice president.
His death leaves Tanzania in an uncertain political situation, according to Nic Cheeseman, professor of democracy at the University of Birmingham.
"The news of Magufuli's death will fundamentally reshape Tanzanian politics. Having dominated the political scene since his election, he leaves a kind of political vacuum," said Cheeseman.
"This will trigger a new uncertainty and all eyes will be on the internal politics of the CCM to see what agreements have been reached within the ruling party regarding the balance of power after the transition."