President Yaradua's Profile: BBC

President Umaru Musa Yar'Adua became the first civilian leader in Nigeria to take over from another after winning controversial polls in 2007.

The former chemistry teacher is also the first Nigerian leader for 40 years to be university educated.

But his academic background appears to have done little to help him on the political stage and mid-way through his first term in office, he was saddled with the nickname "Baba-go-slow".

A reclusive Muslim ex-governor from the northern state of Katsina, he promised a long list of reforms at his inauguration - tackling corruption, reforming the inadequate power sector and the flawed electoral system.

The only point on the to-do list on which he has made some progress is tackling the unrest in the oil-rich Niger Delta.

He met militant leaders and convinced them and thousands of their fighters to give up their weapons during a three-month amnesty in 2009, giving hope of peace at last for the poverty-stricken region.

'In the hands of God'

Yet the issue that has occupied more column inches than anything else during his time in office is his health.

The 58-year-old has suffered from a chronic kidney condition for at least 10 years.

In the past three years he has twice been flown to Germany for emergency treatment and visited hospitals in Saudi Arabia.

In November 2009 he went to a clinic in Jeddah for three months, leaving a power vacuum and intense speculation about the state of his health.

The Niger Delta is the one area Mr Yar'Adua is making progress

His spokesman said he had pericarditis, an inflammation of the lining around the heart.

In his absence, Vice-President Goodluck Jonathan became acting leader in February 2010.

Later that month, Mr Yar'Adua was thought to have returned home from Saudi Arabia to Abuja, although there was still no word on his medical condition.

In previous interviews, the president has refused to say what he suffers from and has repeatedly said that his life is "in the hands of God".

Although he has not yet proved himself a political mover and shaker, he boasts a political pedigree that dates back to the 1960s when his father was appointed as a minister in the post-independence administration.

His late elder brother - an army general - served as deputy leader when Olusegun Obasanjo was Nigeria's military ruler during the 1970s.

The pair were later imprisoned together after they were accused of plotting a coup against late military strongman Gen Sani Abacha.

Self-confessed Marxist

Mr Yar'Adua's emergence as the ruling People's Democratic Party's (PDP) candidate in the presidential election in April 2007 rests almost exclusively on the support of Mr Obasanjo - then the elected civilian president.

Nigerian presidency sources at the time said Mr Obasanjo used a mixture of inducements and threats of investigation by the anti-graft agency to persuade 10 influential state governors to withdraw from the race and back Mr Yar'Adua.

Analysts said that by backing Mr Yar'Adua to succeed him, Mr Obasanjo had hoped to continue pulling the strings after leaving office.

But it has not turned out this way and Mr Yar'Adua has proved to be his own man.

Within months of taking over, he reversed some dubious privatisations of state companies approved by Mr Obasanjo when president - and he also got rid of some key Obasanjo allies in the PDP.

As an undergraduate student in Nigeria's Ahmadu Bello University, Mr Yar'Adua was a self-confessed Marxist and criticised his elder brother's "capitalist" leanings.

During his seven years as Katsina State governor, critics said contracts had gone to companies with links to his family's vast businesses.

Yet he is one of only a few Nigerian politicians to publicly declare their assets - twice before being sworn in as governor and then again when he became president.

He is a father of nine children - five daughters and two sons with his first wife Turai, the first lady, whom he married in 1975 - and two sons with Hajiya Hauwa, whom he married in the 1990s.

He divorced Ms Hauwa in 1997 before first running for governor.

As a governor he was known to have ignored the advice of aides and bodyguards and walked alone to tobacco kiosks to buy a single cigarette.

Described by his critics as taciturn and not known for his tolerance of opposition, Mr Yar'Adua has sometimes been underestimated.

As one commentator put it at the time of his election "because he's quiet, people mistake him for a weakling. But he's someone who knows his own mind".

If he has returned home, Mr Yar'Adua could need every ounce of that will to prove he is fit enough to take centre stage once more on Nigeria's political scene.