As a staff photographer, for one and a half terms, his candid shots of "Dutch" and Nancy loosened the stiff collar of office, and brought humanity and intimacy to the administration.
When George H.W. Bush took over, Souza returned to freelancing. Years later he began covering a young senator from Illinois, who would one day assume the highest office in the land.
Since that day in January 2009, Souza has barely left President Obama's side.
He's toured the world capturing official engagements and private moments. It's arguable that beyond the President's family, there are few who can claim to have had such access during his two terms.
"I don't think there's really anyone else in the White House that has that kind of exposure to him," Souza admits. "I mean, they may know him, the National Security team. They know him from the situation room, and the tense meetings in the Oval Office. But they don't see him interact with his daughter after work, or on a Saturday.
"From a documentary standpoint, I'm the only person that sees him in all these different roles."
Social media changes the game
Whether that's photographing the beloved Bo aboard Air Force One or Jacob Philadelphia, a young African American comparing his hair to Obama's, Souza has been there.
And the public have never been far behind.
"I happened to be the person in this job when all these social media tools came into existence," he says. "I mean, Instagram did not exist before this administration."
Souza's job has transformed immeasurably since his time with Reagan, actively encouraged by the White House to jump on Flickr, Instagram and other platforms, giving him "a chance [to show] some of my documentary photos to the public now, instead of waiting post-presidency." (The White House Instagram account has 2.6 million followers
, while on Flickr Souza and his team have posted over 6,000 images
Earlier this year Souza estimated
he would take approximately two million images by the end of Obama's presidency. So when the administration's second term concludes, how will he look back on his work?
"I've got to say there's so much happening, every day, that it's hard to take time to reflect on things," he says.
"I think any photographer that goes back through their pictures -- whether it's five years later or 15 years later -- brings a different perspective to it. After this is all over and I have a chance to take a deep breath, it'll actually be fascinating for me."