How many years has Barack Obama ruled?

Barack Obama is a president, not a king, so we do not say he has "ruled." Rather, we say he has been "in office." President Obama has been in office since he was elected: he won the election in November 2008 and was inaugurated in January 2009. American presidents serve a four year term, and then they can be re-elected for a second four-year term. Mr. Obama was re-elected in November 2012, so he will serve four more years in office.