He graduated from high school in his hometown (1897) and Slavic philology at the Higher School in Sofia (1903). During his student years he was secretary of the Bulgarian Speech Society at the University. He worked as a teacher at the Second Men's High School in Sofia (1903). He continued his education in Vienna and Germany (1906) under the Slavists V. Jagic, V. Vondrag, M. Reshetar. He met Konstantin Irecek. From 1909 he was curator and director of the National Ethnographic Museum in Sofia (1923–1929). Member and chairman (1926) of the Artistic Council of the National Theater. He has been its director for several months. Corresponding member of the Bulgarian Academy of Sciences (1929). The short autobiographical commentary that the writer makes about himself is interesting: “I appeared in Sofia fifty years ago. I graduated from Sofia University, I would travel all over Europe (unfortunately,
Kostov is one of the most important Bulgarian comedians in the period between the two world wars, who developed and established the various subgenres of comedy in Bulgarian literature after the achievements of Ivan Vazov and Anton Strashimirov.. He is the author of twelve multi-act and five one-act plays. His work is a kind of illustration by means of the comic of negative phenomena and social types in the Bulgarian socio-political and cultural reality between the two world wars. His first publication was the story "Mother's Tears" in the magazine "Drugarka" (Plovdiv) from 1907. His short stories from this period are instructive and instructive, with an interest in folklore humor, proverbs, fables and fairy tales. Kostov collaborates with the newspapers Pryaporets, Novi dni, Vesel Bulgaran, Vecherna Poshta, Zora, Svobodna Rech, Razvigor, etc., where he publishes short humorous stories and feuilletons. He works as a journalist for the Russophile newspaper Sofia Vedomosti. He is a close friend of Prof. Alexander Balabanov , Elin Pelin ,Alexander Bozhinov and others. With a passion for research and a critical attitude, he develops universal themes, such as the thirst for power and wealth, careerism and greed, political chameleonism and unprincipledness. It exposes flaws and vices, emphasizing the socio-economic, psychological and national reality that gave rise to them. In his works, the negative social phenomena after the wars became the object of artistic denunciation by the various means of the comic - humor, irony, satire and grotesque.
The writer raises to a new stage the comedy genre between the wars, enriches its specificity as a technique (labyrinthine comedy) and language (funny jokes, anecdotes, fables and proverbs). His first works are within the limits of vaudeville humor and farcical situations. "Man's Hate" (proposed to the National Theater in 1912 and presented in 1914 after significant revision) caused a scandal and polarized the cultural community with the farcical and ironic attitude of the author to the topic of women's equality. The play evokes associations with Moliere's Scholarly Women.