As the leader of Nigeria's Senate, Bukola Saraki is third in the political hierarchy behind President Muhammadu Buhari and Vice President Yemi Osinbajo.But he has long been seen as having his sights on the top job and has been linked to a string of recent political manoeuvrings that appear to be aimed at weakening Buhari.On Tuesday, Saraki announced his defection to the main opposition Peoples Democratic Party (PDP), citing irreconciliable differences with the ruling All Progressives Congress (APC). What remains to be seen is whether allegations of corruption that have dogged Saraki's rapid rise to prominence will undermine his presidential ambitions."There is no doubt Saraki's profile has been on the rise since he began his political career," said Debo Adeniran of the Centre for Anti-Corruption and Open Leadership lobby group."He has been presidential aide, two-term governor, senator and now Senate president, all within 17 years," he told AFP."The perception that he is corrupt is like an albatross that will continue to haunt him. Nigerians will ask questions when the time comes." Rapid rise Abubakar Bukola Saraki was born on December 19, 1962, into one of Nigeria's wealthiest and most politically prominent families.His father was Abubakar Olusola Saraki, a leading figure in post-independence politics who served as Senate majority leader and was considered a "kingmaker" in his home state of Kwara.He was also chairperson of the Societe Generale Bank of Nigeria, which collapsed in 2006 amid allegations of financial mismanagement that the family denies.The younger Saraki began his political career in 2000 after studying medicine in London and acting as a director of his father's bank.He was appointed to special assistant on budget affairs by president Olusegun Obasanjo before winning election as governor of Kwara state, where he served from 2003 to 2011.During that time, he rose to become chairperson of the powerful Nigeria Governors' Forum, whose views can heavily influence public opinion and the power elite.Allegations Saraki followed a well-worn path from state governor to senator but he defected from the PDP before the 2015 election along with hundreds of parliamentary colleagues.The APC won a historic victory, making Buhari the first opposition candidate to unseat an incumbent president in Nigeria's history.But Saraki's push for the Senate presidency, backed by his former PDP colleagues, put him at loggerheads with the new government and his legal troubles soon began.First he was accused of flouting parliamentary rules to secure the position, then he was charged with failing to disclose all his assets during his time as governor.Prosecutors at the Code of Conduct Tribunal alleged he had acquired wealth beyond his legitimate earnings. Documents submitted to the hearing showed properties in the wealthiest areas of Lagos and London, luxury cars, shares and bank accounts in his wife and children's names.As the case rumbled on, leaked documents in the "Panama Papers" saw him accused of failing to declare offshore assets in his wife Toyin's name.In both cases, Saraki, who was supported in court by dozens of senators and politicians, maintained he had done nothing illegal. Behind the scenes? Further accusations have followed, including that he was linked to a gang that carried out a brutal armed robbery in Kwara state in April that saw 33 people shot dead. Saraki called the claim "baseless".But there soon followed an extraordinary joint statement from lawmakers denouncing Buhari for failing to tackle rising violence and using the security services to target opponents.Saraki's name did not appear on the statement, which was widely interpreted as a threat of impeachment, but many saw his hand in it.That view was reinforced when he used the same language after the Supreme Court threw out the false declaration of assets charges against him.Saraki was also suspected of giving tacit support to a new grouping within the APC, which criticised Buhari's three years in power as a "monumental disaster".* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.