The author of Shuowen Jiezi was Xu Shen.

The Shuowen Jiezi (说文解字) was edited by Xu Shen (许慎) of the Eastern Han Dynasty, and was written around the eighth to twelfth year of the reign of Emperor Yongyuan (永元八年至十二年) of the Eastern Han Dynasty. It was the first language dictionary in Chinese history to systematically analyze the sounds, forms, and meanings of Chinese characters, organized according to their radicals, and one of the earliest character books in the world.

Shuowen Jiezi, as one of the earliest systematic dictionaries in ancient China, not only promoted the standardization and unification of characters at that time, but also profoundly influenced later generations. The theories of philology, the methods of Chinese character study, and the structural laws of Chinese characters summarized in it still serve as a guide and reference for the study and application of Chinese characters in later generations.

Author's Introduction:

Xu Shen was a native of Zhaoling in Ru'nan, and was appreciated as a scholar of the Five Classics without a double Xu Shuzhong. Han Dynasty, a famous scribe, philologist, linguist, is the pioneer of Chinese philology.

Spent at least twenty-one years compiling the world's first dictionary "Shuowen Jiezi" so that the shape of the Chinese characters, sound, meaning tend to standardize. Scholars who honor Xu called Xu Shen Xu Jun and Shuowen Jiezi Xu Xue (说文解字) as Xu Xue (许學). Xu Shen made outstanding contributions to Chinese philology and was honored as the Saint of Characters.

Reference: Baidu Encyclopedia - Shuowen Jiezi