In the early 1600s, various commercial entrepots in maritime Southeast Asia became home to Japanese mercenaries, merchants, and exiled Christians. Their sociopolitical roles in Southeast Asia, and their subsequent exploitation by different (memory) regimes, emphasizes these Japanese as exceptional historical actors and contributes to the trope of the samurai within early modern historiography. Focusing on two icons of this early modern southward expansion—Takayama Ukon, commemorated as “Christ’s samurai,” and Yamada Nagamasa, labeled “the Samurai of Ayutthaya”—this article explores the dynamic trope of Japanese samurai in Southeast Asia and demonstrates how historiography and public diplomacy have created new knowledge and interpretative frames over the centuries. The article’s longue-durée conceptual history critically examines a wide variety of sources, including seventeenth century archival accounts, Japanese imperialist propaganda historiography from the 1930s and 1940s, and more recent public diplomacy, and provides a comparative analysis of how merchant spirit and elite status were used to forge the trope of the Southeast Asian samurai.