Kostis Kotzias (Athens, 1921 – Moscow, 5 November 1979) was a Greek prose writer and playwright. His best-known work is The Smoked Sky, which was also made into a television series on ERT in 1985. He was the brother of fellow writer Alexandros Kotzias.

Kostas Kotzias was born in Athens, the firstborn son of Panagiotis Kotzias from Dimitsana and Xena née Alexandropoulou from Chalkida. His brother is also the writer Alexandros Kotzias. The Kotzias family was wealthy, but was financially devastated during the German occupation, as his father had already died in 1936. He finished high school at Leonteio Lyceum and enrolled in the Medical School of the University of Athens, but interrupted his studies in the last year and after a period of involvement in construction businesses together with his brother, he turned to journalism and literature. Although he studied medicine, he stopped his studies and worked as a builder with his brother for a while. Eventually he devoted himself to literature.

He was a member of EAM and EPON during the period of Occupation and resistance and a founding member of the Union of Young Greek Writers (1943) and later an active member of the left. After the seizure of power by the junta of Colonels George Papadopoulos in 1967, Kotzias fled to Russia. He settled in Moscow, where he wrote and developed a very rich political and anti-dictatorship activity, as a result of which his Greek citizenship was taken away from him until the change of government and its fall. After 1974, his life was divided between Greece and Russia. He died there, from a gastric hemorrhage or stomach perforation, in November 1979.

He made his first appearance in literature with the play The Awakening (1946). This play was staged by the United Artists troupe with Emilios Veakis, while his plays had also been staged by the Tzavalas Karoussos troupe. Then (1947) he collaborated with the Group of Young Writers in the publication of the magazine Themelio. Kotzias himself co-founded the "Realistic Theater" (1949) with George Giannidis and also worked as its director (in the performance School of Women by Moliere). In 1957 he published Smoked Sky, which won the first prize for prose from the Municipality of Athens. In 1946, Kotzias collaborated with Dimitris Photiadis' magazine Eleftheras Grammata. He took over the theater criticism column in the newspapers Demokratiki (1950) and Demokratikos (1951). At the same time, he was involved in journalism: he wrote theater criticism, and after 1974 and the change of government he was a correspondent for Rizospastis in the Russian capital. He also collaborated with the newspapers Aneksartos Typos and Avgi, and Kotzias also collaborated with the magazine Epitheoresis Technis.

Kostas Kotzias' first appearance in the literary field took place in 1957 with the publication of the novel The Smoked Sky, which was awarded the First Prize of the Municipality of Athens. In total, his prose production consists of five novels, two of which (On Ultimate Treason and Aegistos) have a theme inspired by the Plumidis affair.

Kotzias is considered the most important representative of socialist realism in Greece. Kotzias' ideology exerted a great influence on his writings, which mainly deal with the life and struggles of the working class in post-war Athens.