Idriss Deby came to power in 1990 after toppling Chadian President Hissene Habre - with the help of the French secret service.
President Deby has been accused of cronyism and political repression
A shrewd tactician, Mr Deby had been President Habre's chief-of-staff, leading a series of victories over rebel forces in the 1980s and earning a reputation for courage and military prowess.
After six years in office, Mr Deby set up Chad's first multi-party political system and won elections that year.
He was re-elected in 2001, and again in 2006 after amending the constitution, which had previously limited the president to two terms in office.
But Mr Deby, 55, appeared to have little genuine domestic support.
His presidency was dogged by accusations of corruption and political repression, and the 2006 poll was boycotted by opponents who claimed it was neither free nor fair.
He packed his government and armed forces with members of his Zagawa clan, which comprised only 1.5% of the country's 10 million-plus population.
Critics say his single biggest failure was putting his clan before his country.
President Deby became known as a stubborn man who often ignored his advisors. From mid-2006 he suffered a spate of defections of former allies from his own clan to Darfur-based Chadian rebels.
Regionally he has been increasingly viewed with mistrust, and he fell out of favour with Chad's former colonial master France over drilling rights in the 1990s.
President Deby is also thought to have health problems and has been known to fly to Paris for treatment to his liver.