This paper is a case study of early Qing scholar He Zhuo's 何焯 (1661-1722) marginalia found within Hou Hanshu 後漢書. Zhuo was a well-known calligrapher, bibliophile, and textual scholar in the Kangxi period, and during his lifetime, he authored marginalia on hundreds of titles. In the edition of Hou Hanshu held at Peking University Library, 3,700 items have been transcribed by unknown transcriptionists, which mainly contain two kinds of content: (1) Zhuo's comments on historical events, figures, and the text of the Hou Hanshu and (2) collated notes on the text of Hou Hanshu. These marginalia ultimately reveal He Zhuo's accomplishments in the fields of history, historiography, textual criticism, and philology. He Zhuo was also one of the earliest scholars who systematically collated books as well as contributing significantly to the study of textual criticism and the editing of ancient texts, especially Hanshu 漢書, Hou Hanshu, and Sanguo zhi 三國志. However, his reputation was tarnished by fabricated political charges and his scholarly achievements have thus been undervalued. Through examining his scholarly practices and contributions, I hope to rescue him from obscurity within contemporary scholarship and reveal various hidden aspects of intellectual history.