An urban guerrilla is someone who fights a government using unconventional warfare or domestic terrorism in an urban environment.
The urban guerrilla phenomenon is essentially one of industrialised society, resting both on the presence of large urban agglomerations where hideouts are easy to find and on a theory of alienation proper to the modern society of mass consumption.
Michael Collins, a commander of the Irish Republican Army (IRA) is often considered to be the father of modern urban guerrilla warfare. In April 1919 an elite assassination unit, known as The Squad or Twelve Apostles was created in Dublin. The unit was tasked with hunting down and executing British Intelligence operatives in the city, they can be considered one of the first true urban guerrilla units.
Historically guerrilla warfare was a rural phenomenon, it was not until the 1960s that the limitations of this form were clearly demonstrated. The technique was almost entirely ineffective when used outside of the later colonial environment, as was shown by the Cuban sponsored efforts in Latin America during the 1960s culminating in the foco campaign headed by Che Guevara in Bolivia that culminated in his death. The need for the target government to be simultaneously incompetent, iniquitous, and politically isolated was rarely met.
The failure of rural insurgency forced the discontented to find new avenues for action, essentially random terrorism aimed at creating maximum publicity, provoking the targeted regimes into excessive repression and so inciting the general population to join a wider revolutionary struggle. This movement found its mentor in the leader of the ephemeral Ação Libertadora Nacional, Carlos Marighela. Before his death in 1969 he wrote the Minimanual of the Urban Guerrilla which, between the polemics, gave clear advice on strategy and was quickly adopted by others around the world.