<P> Under the fourth Constitution of the Republic of Nigeria, the President is head of both state and government . The President is elected by for a four - year term . In the event of a vacancy the Vice President serves as Acting President . </P> <Dl> <Dt> Status </Dt> </Dl> <Table> <Tr> <Th_colspan="3"> President </Th> <Th_colspan="3"> Term of office </Th> <Th> Political party (at time of election) </Th> </Tr> <Tr> <Th> No </Th> <Th> Portrait </Th> <Th> Name </Th> <Th> Took office </Th> <Th> Left office </Th> <Th> Duration </Th> </Tr> <Tr> <Th> 12 </Th> <Td> </Td> <Td> Olusegun Obasanjo (1937--) </Td> <Td> 29 May 1999 </Td> <Td> 29 May 2007 </Td> <Td> 7003292200000000000 ♠ 8 years, 0 days </Td> <Td> People's Democratic Party </Td> </Tr> <Tr> <Th> 13 </Th> <Td> </Td> <Td> Umaru Musa Yar'Adua (1951--2010) </Td> <Td> 29 May 2007 </Td> <Td> 5 May 2010 (died in office .) </Td> <Td> 7003107200000000000 ♠ 2 years, 341 days </Td> <Td> People's Democratic Party </Td> </Tr> <Tr> <Th> 14 </Th> <Td> </Td> <Td> Goodluck Jonathan (1957--) </Td> <Td> 5 May 2010 </Td> <Td> 29 May 2015 </Td> <Td> 7003185100000000000 ♠ 5 years, 25 days </Td> <Td> People's Democratic Party </Td> </Tr> <Tr> <Th> 15 </Th> <Td> </Td> <Td> Muhammadu Buhari (1942--) </Td> <Td> 29 May 2015 </Td> <Td> Incumbent </Td> <Td> 7002998000000000000 ♠ 2 years, 267 days </Td> <Td> All Progressives Congress </Td> </Tr> </Table> <Tr> <Th_colspan="3"> President </Th> <Th_colspan="3"> Term of office </Th> <Th> Political party (at time of election) </Th> </Tr>

Who is the highest serving president of nigeria
find me the text answering this question