The unnamed 44th President of the United States succeeded George W. Bush as President, serving for one-term from January 20, 2009 to January 20, 2013.
He was elected in the 2008 presidential election. It is unknown which political party he belonged to. If he was a Republican, then he would've been defeated by Garrett Walker in the 2012 general election, or chosen not to run for re-election. If he was a Democrat, then he may have been defeated by Walker in the primaries, or chosen not to run for re-election. Either way, he left office in 2013 and Walker became the 45th President.
At Walker's inauguration in Chapter 1, he is briefly seen sitting behind Walker during the inaugural address.