U.S. intelligence experts are trying to build a profile of Kim Jong Un to give President Donald Trump a competitive edge in one of the most consequential summits since the Cold War, but they face a huge challenge — figuring out a secretive North Korean ruler few people know much about.

Following a long tradition of arming U.S. presidents with political and psychological dossiers of foreign leaders ahead of critical negotiations, government analysts are gathering every new bit of information they can glean about Kim and making adjustments to earlier assessments of what makes him tick, U.S. officials said.

They will rely in part on the impressions drawn by CIA director Mike Pompeo, who just weeks ago became the first Trump administration official to meet Kim. Pompeo, Trump's pick to become secretary of state, came back from Pyongyang privately describing the young North Korean leader as "a smart guy who's doing his homework" for the meetings, according to one U.S. official, who described Pompeo's personal view of Kim for the first time.