The academy-trained painter Oskar Herman left for Munich in 1904, where he attended the school of Anton Ažbe for a while, ultimately enrolling at the Art Academy and studying under professors Herterich, Habermann, Raupp and Halm from 1904 until 1910. He was the first representative of the "Munich Circle" of Croatian art (along with Becić, Kraljević and Račić). Herman mostly resided in Munich until 1933, making short visits to Zagreb, Belgrade, Paris and the south of France. He then returned to Zagreb in 1934 and stayed until 1941. During World War II, Herman moved to Ljubljana, but was deported to a prisoner camp in Calabria. After being freed from the camp in 1943, he joined the resistance's National Liberation Army and worked in the Art Colony in Cozzano (Apulia). In 1944, Herman returned to the liberated city of Split and afterwards to Zagreb.

His works are characterized by an exploration of coloristic harmony, with the shapes of his images mainly depending on color. His complete oeuvre is marked by richness of color and an expressionist restless stroke of the brush. He paints in order to express the world of feelings and testify to man's pain and vulnerability, developing authentic painting with gorgeous and harmonious colors, expressive forms, balanced drama and calmness, sensuality and poetics. Prone to distortion, he shapes human figures, figural compositions and landscapes with masses of paint and winding lines, sporadic still lifes from the beginning made in oil and drawing (chalk, pencil, charcoal, ink), in 1920 in watercolor, from 1938 in gouache and tempera.