“Hyperaspistes” is the name of an anonymous critic of the Meditations. The word derives from the Greek word for “champion” or “defender” (CSMK 188 n. 1). In the collection of letters assembled by Clerselier (vol. 2), it is Letter XV that is from a man calling himself “Hyperaspistes.” A version of this letter is found in volume 3 of the Adam and Tannery collection (AT III 397–412). However, unlike Letter XV of the Clerselier collection, the Adam and Tannery letter does not explicitly identify Hyperaspistes as the author (although it is speculated in a footnote). Versions of Descartes’ reply are also included in both the Clerselier and the Adam and Tannery collections (AT III 422–35, CSMK 188–97). There appears to have been a precedent for the use of the pseudonym “Hyperaspistes.” It is found, for example, in the title of a book written by Johannes Kepler (1625), in which Kepler dubs himself “Hyperaspistes” or “defender” of Tycho Brahe.

Some have speculated that Hyperaspistes was a physician or perhaps a priest interested in philosophy, for in his objections to Descartes he mentions his encounter with a blind man among “our three hundred blind men living at Paris” (AT III 409). Some, including Baillet, believed this to be a reference to the Hôpital des Quinze-Vingts, a Paris almshouse for the blind. This and other clues led Baillet to speculate that Hyperaspistes was very likely a man by the name of M. Porlier (Agostini 2003, 8). Igor Agostini (2003, 7) argues against Baillet's conclusion. Other scholars have speculated that Hyperaspistes was a member of a group of natural philosophers associated with Pierre Gassendi, author of the Fifth Objections. In the Adam and Tannery collection, Hyperaspistes’ objections are made in a letter dated July 1641 (AT III 397–412). The letter is written in Latin and includes fourteen objections. Descartes expresses to Hyperaspistes the possibility of including the exchange in the first printing of the Meditations (AT III 422, CSMK 188). But their exchange did not make it into the final printing.