The Revolutionary Armed Forces of Colombia (FARC), the country's oldest rebel group, has been embroiled in conflict with government forces for nearly five decades.
The cat-and-mouse violence had been believed to be coming to an end after government troops killed several of FARC's leaders in recent years - but the rebels have proven far from defeated, staying in mountainous and jungle regions and using guerrilla styles reminiscent of Che Guevara's.
Al Jazeera's Karl Penhaul tracked down one of FARC's fighting units, spending 10 days among the group to learn more about their motivations, goals and tactics.
This is part 1 of an exclusive 2 part series. Part two is available here.