He was a graduated geologist, and worked for YPF for some time. He soon abandoned that work, and wrote some child books. He soon jumped to comic books (or "historietas", as they are known in Argentina), and created the series Sargento Kirk and Bull Rocket for Editorial Abril. He saw the potential in the genre and started his own editorial, Frontera, and started with literary books about Kirk and Rocket. To negotiate his departure from Abril he gave up the right to Bull Rocket,note and kept Kirk. Frontera published Anthology Comic series as well, such as "Hora Cero", "Hora Cero Semanal" and "Hora Cero Extra".
Frontera was a success, and introduced several new characters, such as Ernie Pike, Ticonderoga, Randall the Killer, Rolo el Marciano Adoptivo, Sherlock Time, etc. The most successful one, however, was El Eternauta, with Solano López. It was the story of an alien invasion set in Buenos Aires: so far all the comics were set in the US. The story lasted for two years, from 1957 to 1959, and was reedited several times, even abroad.
Frontera was closed, and Oesterheld moved to other editorials. Abril sold the "Misterix" comic to Yago, and Oesterheld created Mort Cinder in it, alongside Alberto Breccia. He also created other short-lived characters.
Since this point, his works became more politically loaded. He wrote a biopic of Che Guevara and started another about Eva Perón, but all the comics were seized by the military government and the project was cancelled. He wrote a remake of El Eternauta where the aliens were allied to the world powers, but it was cancelled so he rushed the ending. Far from just writing comics, he joined the terrorist organization Montoneros as spokeman. He wrote another comic for the Noticias newspaper, La Guerra de los Antartes, which was also cancelled when the military government closed the newspaper. He wrote a sequel for El Eternauta, but by this time he was on the run, fearing reprisal for his Montoneros membership. He did not even meet with Solano Lopez at this time, and explained the plots and scenes by phone. At some point he was captured and forcibly disappeared, but the story was completed.
There was a long legal battle after his death between his widow Elsa, editorial Record and artist Solano López over the rights of his most successful creation, El Eternauta.
Works created by Héctor Germán Oesterheld include:
- Bull Rocket
- Sargento Kirk
- Rolo, el Marciano Adoptivo
- Ernie Pike
- El Eternauta
- Sherlock Time
- Mort Cinder
- Evita: Vida Y Obra de Eva Perón
- La Guerra de los Antartes
- El Eternauta: Segunda Parte
Tropes featured in Héctor Germán Oesterheld's works include:
- Alien Invasion: "El Eternauta" is the most known one, but "La Guerra de los Antartes", "Sherlock Time", "Rolo, el Marciano adoptivo", etc; also feature it.
- Author Avatar: Ernie Pike has the same face of Oesterheld. It was initially unintended, as Pratt misunderstood Oesterheld's instructions when he first draw the character,note but Oesterheld liked the result and let it stay. He appears as himself in "El Eternauta", as a mere witness who heard Juan Salvo's story and thought that "I Should Write a Book About This". In the second story, he upgrades himself to narrator protagonist, sidekick of the lead character.
- Follow the Leader: When Oesterheld began his works all pop-culture fiction for the mass public was set in the United States. A fictional character from Argentina was basically an unheard of concept. So, despite being from Argentina, his initial characters such as Bull Rocket, Ernie Pike and Sargento Kirk were all American. He first toyed with the idea with Rocket's "Buenos Aires no contesta", with the action moving to Argentina, and "El Eternauta" was his first work fully set in Argentina from the let go.
- God Does Not Own This World: He had to sell the rights over "Bull Rocket" to be able to end his contract with Abril and work in Frontera instead. Abril continued with Bull Rocket, with new artists.
- La Résistance: The vast majority of his works involve it at some level. More so when Oesterheld joined the Montoneros.
- Self-Adaptation: "El Eternauta", "Bull Rocket" and "Sargento Kirk" have been adapted into literary books. Also written by Oesterheld.
- Small Reference Pools: During the '70s Oesterheld joined the left-wing guerrilla organization Montoneros, and was forcibly disappeared in 1977 shortly after finishing writing El Eternauta II, the sequel of "El Eternauta". As a result, his life's story and tragic fate is now known by many people who had never actually read comics.
- Stillborn Franchise: Oesterheld and Breccia made a biopic of Che Guevara, Life of Che, and intended to start a series of biopics about other populist figures in South America. The military dictatorship banned the comic and seized all the unsold editions, as well as all of the copies of HGO's unpublished sequel about Eva Perón. The plan for further comic biopics was thus abandoned by Oesterheld and Breccia (democracy was briefly restored in 1973, but they did not try to resume the project). Both comics were re-published posthumously some decades later, when the political conflicts were over.