Jakaya Kikwete has been president since 2005 and is now serving his second term, having won re-election in October 2010.
He has won much international praise for his management of the Tanzanian economy, but his political power base was undercut at the 2010 election when he won 61% of the vote on a low turnout of 42%, down from the 80% he won in 2005 on a turnout of 72%.
The main opposition Chadema party, whose candidate finished closest to Kikwete, rejected the 2010 outcome, alleging fraud.
Mr Kikwete served as foreign minister in 1995-2005. As chairman of the African Union he played a significant role in finding a solution to the post-election chaos in neighbouring Kenya in 2007.
He is a veteran of the Chama Cha Mapinduzi (CCM) party, which has run Tanzania since independence, and has steered the country towards a free-market economy without totally rejecting the socialist principles of founding President Julius Nyerere.
Mr Kikwete, a former army officer, was born in October 1950 and is married with eight children.
His predecessor Benjamin Mkapa retired after 10 years in power. He was credited with being the driving force behind Tanzania's extensive economic liberalisation, which was well received by the IMF and World Bank.
Under his presidency inflation dropped, the economy grew and Tanzania's foreign debt was wiped. But then as now, government critics say most Tanzanians remain impoverished.