Carlo Zen is the pseudonym of a Japanese novelist, manga writer, and game scenario writer. The author maintains a high degree of anonymity, and no verified personal details such as real name, age, or gender have been publicly disclosed. The pseudonym is derived from Carlo Zeno, a 14th-century Venetian admiral known for his strategic naval command, with Zen adopting the Venetian variant of the surname.

Zen began their career by serializing what would become their debut work, The Saga of Tanya the Evil, on the user-generated novel website Arcadia. The series gained attention there before being acquired for print publication, with the first light novel volume released by Enterbrain in October 2013. This marked the official start of their professional writing career. In April 2019, Zen became a member of the Science Fiction and Fantasy Writers of Japan.

The body of work spans several light novel series, manga series as an original creator, and video game scenarios. The light novel series The Saga of Tanya the Evil remains the flagship work, with ongoing publication that had reached fourteen volumes. Other novel works include the four-volume Yakusoku no Kuni, the single-volume tie-in Seventh Dragon 3 UE72 Mikan no Yūma, the collection Jyūma Taisen Okotahakarigoto Renri, and the science fiction series Yakitori: Soldiers of Misfortune, which began publication in 2017. As a manga original creator, Zen has overseen adaptations of The Saga of Tanya the Evil as well as original series such as Baikoku Kikan, Terror-kyōju no Ayashii Jugyō, and Ashita no Teki to Kyō no Akushu o.

The Saga of Tanya the Evil has been adapted into multiple formats, establishing Zen as a significant figure in contemporary anime and manga production. The series received an anime television adaptation that first aired in 2017, followed by an animated feature film in 2019. A second anime season has been announced. The franchise expanded into the crossover comedy series Isekai Quartet, which unites characters from The Saga of Tanya the Evil with those from other popular isekai properties. Zen is credited as an original creator for the character Tanya Degurechaff in both seasons of Isekai Quartet and the theatrical film Gekijōban Isekai Quartet: Another World. The Yakitori novel series also received an anime adaptation in 2023.

Recurring elements within Zen’s work include a focus on military strategy, geopolitical maneuvering, and alternate history. The Saga of Tanya the Evil is noted for its depiction of an alternate version of World War I-era Europe, with a protagonist who applies rationalist and modern corporate management philosophy to military command. The writing often incorporates detailed tactical analysis, philosophical debates regarding rationality and faith, and a cynical tone. This combination of isekai conventions with historical military fiction established a distinctive artistic identity that contributed to the broader popularity of the series.

Zen holds a significant position within the light novel and anime industries as a creator whose work achieved both critical recognition and commercial success, with the franchise expanding across multiple media and being licensed for international release in English by Yen Press. The continued publication of new light novel volumes and manga series, along with the production of additional anime adaptations, demonstrates an enduring creative presence.