Subcomandante Insurgente Marcos describes himself as the spokesperson for the Zapatista Army of National Liberation (EZLN) but, since he is so prominent a figure, he is considered by many to be one of its main leaders.

According to the Mexican government, Marcos' real name is Rafael Sebastián Guillén Vicente. Guillén studied high school at Instituto Cultural Tampico, a Jesuit school in Tampico, Tamaulipas, where he became acquainted with Liberation Theology. He later moved to Mexico City where he graduated from the Metropolitan Autonomous University (UAM), then received a masters' degree in philosophy at the National Autonomous University of Mexico (UNAM) and began work as a professor at the UAM. After that he left to begin his revolutionary activity. While Marcos has always denied being Rafael Guillén, Guillén's family are unaware of what happened to him and they refuse to say if they think Marcos and Rafael are the same person or not. During the Great March to Mexico City in 2001, Marcos visited the UAM and during his speech he made clear that he had at least been there before.

Like many of his generation he was radicalised by the events of 1968 and became a militant in a Maoist organisation. However, the encounter with the outlook of the indigenous peasants of Chiapas transformed the Zapatistas' ideology, and Marcos has embraced an approach to social revolution that has been described by some as post-modernist; others argue that his philosophies and actions are more closely related to the revisionist Marxist ideals of Antonio Gramsci that were popular in Mexico during his time at university.

Marcos in his own words:

Marcos is gay in San Francisco, black in South Africa, an Asian in Europe, a Chicano in San Ysidro, an anarchist in Spain, a Palestinian in Israel, a Mayan Indian in the streets of San Cristobal, a gang member in Neza, a rocker in the National University, a Jew in Germany, an ombudsman in the Defense Ministry, a communist in the post-Cold War era, an artist without gallery or portfolio.... A pacifist in Bosnia, a housewife alone on Saturday night in any neighborhood in any city in Mexico, a striker in the CTM, a reporter writing filler stories for the back pages, a single woman on the metro at 10 pm, a peasant without land, an unemployed worker... an unhappy student, a dissident amid free market economics, a writer without books or readers, and, of course, a Zapatista in the mountains of southeast Mexico. So Marcos is a human being, any human being, in this world. Marcos is all the exploited, marginalized and oppressed minorities, resisting and saying, 'Enough'!

Much of his writings – articles, poems, speeches and letters – have been compiled into a book: Our Word is Our Weapon.

In December 2004, he announced plans to write a book, called Muertos incómodos (Awkward Dead), in conjunction with crime writer Paco Ignacio Taibo II .