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He grew up in Prlekija. He studied Slavic Studies in Vienna and Ljubljana. In Ljubljana he also studied comparative literature and literary theory. Among other things, he was the editor and secretary of Kosovel's "Mladina", the artistic director and director of "Delavski oder" in Ljubljana, and the director of the National Theater in Ljubljana. He was a professor of contemporary Russian literature at the Faculty of Arts and a corresponding member of Yugoslav Academy of Sciences and Arts (JAZU). He received the Prešeren Award three times.
As a playwright, Kreft preferred topics from Slovenian history. Rather than individual fates, he was interested in the relationships between social classes.
Among his major plays are:
- Celjski grofje
- Velika puntarija
- Kranjski komedijanti
- Balada o poročniku in Marjutki
- V ječi življenja.