An American service member was believed to be in North Korean custody on Wednesday after willingly crossing into the nuclear-armed country, despite a “do not travel” advisory by the U.S. State Department due to the risk of arrest and long-term detention.

But the service member, Travis King, was far from the first U.S. national to venture into or be detained by the reclusive country.

Numerous U.S. citizens — including soldiers, tourists, journalists and scholars — have been detained or crossed into North Korea since the Cold War.