Tyrion Lannister refers to his book An History of the Great Sieges of Westeros when preparing the defense of King's Landing. Varys criticizes him as an uninspired writer. Tyrion and Bronn debate how to correctly pronounce his name, but Varys offhandedly reveals the proper form: "sh(uh)-VY-al-thun".
Archmaester Ebrose hands his book An History of the House of Lannister to Samwell Tarly, claiming that it might be useful when writing A Chronicle of the Wars Following the Death of King Robert I. He criticizes Ch'Vyalthan for his writing, but praises him for his research.
In the books
No mention of an Archmaester Ch'Vyalthan is made in the A Song of Ice and Fire novels.