Warring States diplomat and strategic adviser (zònghéngjiā 縱橫家), active ca. 320–284 BCE. Native of Luoyi 雒邑 (Eastern Zhou capital). Tradition credits him with organizing the Six-State Alliance (héng 縱) against Qin; the Mawangdui manuscript (戰國縱橫家書, KR3h0106) presents a substantially different picture in which his career was primarily as an undercover agent (jiàn 間) working on behalf of Yan 燕 to weaken Qi 齊. Executed in Qi ca. 284 BCE after the exposure of his covert operations. His dates (ca. 380–284 BCE) follow Wilkinson, Chinese History: A New Manual (§27.1.3). The received biography in Shiji 史記, juan 69, conflated the historical Su Qin with an earlier homonymous figure; the Mawangdui text allows the two figures to be disentangled. Su Qin’s letters in KR3h0106 are addressed primarily to King Zhao of Yan 燕昭王 (r. 311–279 BCE). No CBDB entry located for the pre-Qin period.