Italian physician and philosopher lived at Mantua in the sixteenth century. A philosophical work of his on the articles of belief, entitled "Meor ha-Golah" (The Light of the Exile), is still extant in manuscript (Michael, "Or ha-Ḥayyim," No. 383). Castel d'Ajano is supposed to be the author of the liturgical poem 
("For the Comfort of a Poor Captive"), which bears the signature 
(Roman Maḥzor, 2:162b). He shows considerable knowledge of the Talmud in a casuistical note on a passage in R. Nissim's commentary on Megillah, which is still extant in manuscript (Neubauer, "Cat. Bodl. Hebr. MSS." No. 911,8b).
It is likely that Samuel di Castel d'Ajano is identical with Samuel Castiglione, who, at the same epoch, practised as a physician at Mantua, and was also a liturgist (compare Zunz, "Literaturgesch." p. 417).