[citation needed] Through his comics, Oesterheld criticized the numerous military dictatorships that beleaguered the country in different periods ranging from 1955 to 1983, as well as different facets of capitalism, colonialism and imperialism, choosing a subtle criticism in his early comics during the 1950s and early 1960s, and a stronger and direct approach in his later work, after the execution of Che Guevara in 1967, and onwards from then on: in 1968 he wrote a biographical comic book of Che Guevara, which was subsequently banned and destroyed—later republished (and for the first time in complete form) in 2008—by the ruling military dictatorship self-styled as "Argentine Revolution" (1966–1973).

HGO continued to publish works in clandestine form while hidden in secret locations, but he was ultimately kidnapped and disappeared in 1977.

His publishing house closed five years later due to a combination of the economic crisis sweeping Argentina in the 1960s, foreign competition, and the exodus of Argentine comic artists to Europe.

His 1968 biography of Ernesto 'Che' Guevara, a year after Che's death, was removed from circulation by the government and the originals destroyed.

In 1977 his daughters, Diana (23), Beatriz (19), Estela (25) and Marina (18), were arrested by the Argentine armed forces in La Plata.

She became one of the spokeswomen for the Grandmothers of the Plaza de Mayo, which advocates for the return of children of the "disappeared" to their birth families.

When the Italian journalist Alberto Ongaro enquired about Oesterheld's disappearance in 1979, he received the reply: "We did away with him because he wrote the most beautiful story of Ché Guevara ever done".

In a report to the Argentine National Commission on the Disappearance of Persons, which published its findings in 1984 entitled Nunca Más, Eduardo Arias recalls seeing Oesterheld between November 1977 and January 1978.

Oesterheld worked with artists including Hugo Pratt, Alberto Breccia, Francisco Solano López, Ivo Pavone, Dino Battaglia, as well as Horacio Altuna, José Massaroli, Eugenio Zoppi, Paul Campani, Gustavo Trigo, Julio Schiaffino and others.