From the 1960s, Yoo Youngkuk painted mountains day in and day out earning him the nickname ‘Mountain Painter’. Since he was a child, he has experienced firsthand in his hometown of Uljin and wanted to capture the familiar nature that was next to him on the canvas. However, The mountains in Yoo’s works are not realistic representations, but rather archetypes of nature, emblems of a ‘concept’ that signifies the sublime beyond human reach, and the ‘essence’ of Koreanness. To convey this idea, the artist devoted his entire life to experimenting with colors and forms. As pursuing the unity of art and nature, he aimed to present an ideal and harmonious world with the use of the most basic formal elements - dot, line, and plane. While adopting Western painting conventions, his works centered on nature, a prominent theme in Eastern art, enabling the artist to develop a distinctive artistic style.

His paintings were characterized by a rough texture of paint and strong organic shapes in the late 1950s and early 1960s, but they became more monotonous with geometric shapes and an emphasis on colors in the late 1960s. The division of the canvas into ascending and descending planes created by the diagonal structure generates both tension and balance, revealing a solid structure and dynamics. In the 1970s, he incorporated more shapes and lines into his works, partitioning canvases even further. After 1972, the sharp edges were changed to rounded angles, and triangular shapes that implied the images of 'mountains' more explicitly, suggesting the coexistence of abstractness and concreteness.