When people get one of their first looks at the rivals standing side by side Wednesday, they'll see a Republican who is 14 years older and an inch taller than the 51-year-old president, who stands 6-feet-1.
Obama and Romney first met in 2004 at a gathering of Washington's political and media elite. Romney, then governor, and Obama, a senator-elect from Illinois, were picked by the Gridiron Club to deliver speeches at the group's dinner. The private event's festive atmosphere, however, meant their dueling speeches were more about cracking jokes than outlining their policy differences.
By the time their paths crossed again, the rising political stars were presidential contenders. Seeking to line up votes in the New Hampshire primary, they both showed up for the 2007 Labor Day parade in the town of Milford. They shook hands, exchanged a few pleasantries and turned their attention to the voters.
New Hampshire was also the site of what aides to both men believe was their last face-to-face meeting before Wednesday's debate.
In January 2008, the Republican and Democratic primary candidates were holding back-to-back debates in Manchester. After the Republicans wrapped up, the moderator invited the Democrats waiting in the wings to join them briefly onstage for a brief show of bipartisanship.
Obama and Romney found each other in the scrum. They smiled and shook hands, with Obama placing his hand warmly on Romney's arm.
Obama went on to win the White House. Romney dropped out of the Republican race shortly thereafter.