Either one or a group of Korean War-era heroes who were "lost" near Pyongyang. Slugger the Junior Dynamo was rumored to have been a part of the Commando K project.
Commando K destroyed Fafnir in Alaska, a dragon like robot creation built by Dr. Gearbox to aide his escape from Soviet Russia, though his intentions were misinterpreted by the U.S. Authorities.
It's not known for sure if Commando K was just one hero or a group of some kind of advanced soldiers. The headline is vague. And the mention in A Visitor's Guide about Slugger being a part of the project again could mean that the project was an elite unit of soldiers.
Also unknown is whether or not getting "lost" was Commando K's final fate or merely a temporary one.