When photographer Mark Seliger walked into a room at the Bush Center in Dallas this past July, he faced George W. Bush and Bill Clinton, two former U.S. Presidents who had just announced a new educational joint venture between their respective libraries. The unprecedented photoshoot — Seliger had photographed presidents before, but never two at the same time — is just one of the many TIME commissioned this year.
The subjects of those portraits include Republican frontrunner Donald Trump, new Late Show host Stephen Colbert, actors like Tom Hanks and Sandra Bullock, astronaut Scott Kelly and many more of the year's most influential leaders in politics, entertainment, business, sciences and the arts. And they weren't all celebrities: TIME also photographed the women who fight the Islamic State in Syria and the families who continue to flee the group's regime of terror.
In this chronological gallery, TIME's photo department presents its selection of the best portraits it commissioned in 2015.