This article reexamines the life of Dr Oskar Frankfurter (1852–1922), co-founder and president of the Siam Society from 1906 to 1917. Despite his impactful contributions to Thai studies and culture during his tenure as chief librarian of the Vajirañāṇa National Library, his life remains shrouded in obscurity. Drawing from recently discovered archival sources in Thailand, Germany, and the UK, the article explores Frankfurter’s early years in Hamburg, his influential career in Siam from 1884 to 1918, and his role in establishing Thai Studies in Germany. The narrative is structured to cover key life phases, offering a glimpse into the fascinating legacy of this forgotten luminary.