Jacobo Arenas ("nom de guerre" of Luis Morantes) was a Colombian guerrilla and ideological leader of the Revolutionary Armed Forces of Colombia (Fuerzas Armadas Revolucionarias de Colombia, FARC). He was also one of the FARC figures involved in the organization and creation of the Patriotic Union political party in 1985. He was fluent in several languages other than his native Spanish, including English and Russian.
Jacobo Arenas spent most of his life involving himself in the activities of Marxist revolution in Colombia since the 1960s.
Arenas is credited for helping to lay the foundation for the FARC's organizational structure and promoting its later development into what is usually considered as one of the strongest and longest lasting Marxist guerrilla movements in the world. To implement the policy of "standing steadily", he taught them in several areas, such as anthropology, international military law and counter techniques for any changing situation.