Early-Táng exegete and philologist, given name Zhòu 籀, zì Shīgǔ 師古 (which became his customary name), of Wànnián 萬年 in Yōngzhōu (greater Chángān). Grandson of Yán Zhītuī 顏之推, author of the Yánshì jiāxùn 顏氏家訓, and a key figure of the family’s Sui–Tang philological line; his nephew was the calligrapher Yán Zhēnqīng 顏真卿. Held offices including Tōngzhí láng, Mìshū jiàn, Hóngwénguǎn xuéshì, and was on the editorial board of the Wǔjīng zhèngyì. He produced the canonical commentary on the Hànshū (presented 645), drawing on twenty-three earlier commentators; the work fixed the standard reading of the Hànshū for a millennium. He further annotated the Jíjiù piān KR1j0017 and authored Kuāngmiù zhèngsú KR1j0009 (presented posthumously 651 by his son Yán Yángtíng), a foundational Táng work of philological criticism. As the Sìkù tíyào on the Kuāngmiù zhèngsú observes, Yán’s lack of historical awareness about pronunciation — he treats medieval and Hàn rhyme-categories as continuous — paradoxically opened the door to the later doctrine of xiéyīn 叶音 that the Qing scholar Gù Yánwǔ had to combat. CBDB lifedates 581–645, in agreement with the JiùTángshū biography (juàn 73).