Who was the Vice President under Barack Obama?

Joe Biden served as the Vice President under Barack Obama from 2009 to 2017. During this time, he played a significant role in the administration, contributing to various policies and initiatives, including economic recovery efforts and healthcare reform. Biden's long tenure in the Senate prior to becoming Vice President equipped him with considerable experience in legislative matters, which he leveraged to support Obama’s agenda.

The other figures listed were not Vice Presidents under Obama. George H.W. Bush served as Vice President under Ronald Reagan and later became President. Mitt Romney has never held the office of Vice President; he was the Republican nominee for President in 2012. Al Gore served as Vice President under Bill Clinton from 1993 to 2001, making him another prominent political figure, but not part of the Obama administration. Thus, Joe Biden is the only correct answer among the options provided.