Marquis Andras has his origins as a demon in the medieval grimoires. One of Andras' earliest known appearances as a demon is from the Fasciculus Rerum Geomanticarum (15th century) and the Pseudomonarchia Daemonum (1577). Most of the information from this book appears to have been copied by the author of the Ars Goetia (mid-17th century), a section from the book Lesser Key of Solomon, also known as the Clavicula Salomonis Regis or Lemegeton.
Andras is the 63th demon listed in the Ars Goetia and is described as a Great Marquis of Hell that commands thirty legions of demons. He appears with a winged angel's body and the head of an owl or raven, riding upon a strong black wolf and wielding a bright sword. His description in the Pseudomonarchia Daemonum also notes Andras might attempt to kill his conjurer if no sufficient precautions are taken.
The name "Andras" appears to be derived from the angel Andas, "one of the angels of the third month that is called Sivan" from the Liber Juratus Honorii or The Sworne Booke of Honorius (13th century or earlier). Notably, Andas is not mentioned to be a fallen angel but appears to have received the label of demon in later grimoires.
Although unclear, certain characteristics of Andras appear to align with the images of certain celestial bodies as described in the Picatrix (c. 1,000 AD), which includes material used by later grimoires. Namely, him being a man with the head of a bird, riding upon animal with a sword in his hand. Andras' appearance in Castlevania: Portrait of Ruin appears to be based on an illustration from the 1863 edition of the Dictionnaire Infernal.