O Se-ch’ang(1864-1953) was a pioneering enlightenment thinker, independence activist, calligrapher, and leading intellectual of Korea's modern era. As the compiler of Geunyeok seohwi (Compiled Calligraphy of Korea) and Geunyeok hwahwi (Compiled Paintings of Korea), he exerted a profound influence on the shaping of traditional Korean art collections during the transitional period into modernity. O actively engaged in the collecting practices of his contemporaries directly in the field. However, despite his extensive influence, his role behind the scenes of the antiquities trade remains difficult to discern from today's perspective. By synthesizing scattered records including colophons (jebal) inscribed on artworks, contemporary publications, and the reminiscences of collectors, this study reconstructs O's activities and delineates his specific roles. In particular, it delineate O’s role by focusing on the collecting practice of Pak Yŏng-ch’ŏl and Chŏn Hyŏng-p’il, the two representative collectors in the colonial era who amassed grand-scale art collection under O’s guidance.The 1930s, when Pak and Chŏn were most active, marked the “Golden Age” of the antiquities trade. Behind the burgeoning market lay a historical shift in which Korean collectors emerged at the forefront to establish monumental collections. As they built their new collections of traditional Korean painting and calligraphy, O provided a foundational bedrock by transferring ownership of his own prized pieces. Furthermore, rooted in his profound erudition, he offered the professional connoisseurship and authentication required by these collectors. At the center of network for art collecting, he also served as an intermediary, thereby catalyzing the formation of these collections. Ultimately, O’s multifaceted role carried profound significance for cultural transmission, preserving the rich tradition of collecting traditional Korean painting and calligraphy and passing it down to modern collectors. In this regard, O Se-ch’ang truly epitomized the “master of collecting traditional Korean painting and calligraphy.”