Sen. Marco Rubio, Florida
The freshman senator was elected to the Senate in 2010 with support from the conservative Tea Party wing of the party. The son of Cuban-American immigrants, he, too, was considered a top contender for Romney's running mate.
Not only a rising star in the Republican Party, Rubio is a prominent Hispanic, a group Romney is struggling to appeal to but hopes to make inroads with this election. Romney took a hard-right stance on immigration during the primary, backing the concept of self-deportation, but he has largely avoided the issue after clinching the nomination and elevating the role of prominent Hispanics, including Rubio.
Other than Romney, obviously, Rubio will have one of the most prominent roles at the convention. He will set the stage for the main act, Romney, by introducing the Republican candidate Thursday night at 10 p.m. ET.