This paper focuses on the main characters of the last play by Portuguese playwright Antonio Jose da Silva (1705-1739) - Precipicio de Faetonte [Phaetons' Fall] (1738), with which the main characters of his penultimate play, As variedades de Proteu [Proteus varieties] (1737), are sometimes compared. As mythological characters, we trace the characters' construction of Faetonte and Egeria in the predecessor Classical and Iberian literature, to identify the mythical roots appropriated by Silva in his dramaturgy. In order to compare Faetonte's character construction, we also have searched for references about Proteu, in the homonymous work. As these myths are very sparse in the Greco-Latin tradition, we searched ancient authors who mentioned these characters. By comparing this corpus with the ancient texts and other plays by Silva, we realized that he achieved creative emancipation when dealing with lesser-known myths in the 18th-century Portuguese imaginary, which also allowed him greater flexibility in dealing with the precepts that govern the tragicomic genre, to which his writing adheres.