The story of Castiel begins with a Google search. In 2015, "Supernatural" showrunner Eric Kripke (who now runs "The Boys" on Amazon Prime Video) tweeted, "#SPNFunFact We were airing on Thursdays & needed a new character name. I googled 'Angel of Thursday' (for luck): got Castiel." Kripke was referencing the fact that the show famously used to air on the CW on Thursday nights. A similar search did not return a close match for Castiel here at Looper, so we'll have to take Kripke's word for it.
The "Supernatural" mythology is a hodgepodge of folklore, religious myth, and its own imagination, so while an angel with a similar name to Castiel's does exist in Hebrew scripture, it's unclear whether that character was the inspiration for "Supernatural's" Cas. The angel Kafziel, whose name does bear an uncanny resemblance to Castiel's, is described by the Zohar (an ancient work of Jewish mysticism) as one of the chief aids to the archangel Gabriel.
While many biblical angels have, throughout millennia of translated texts and new writings, undergone countless variations upon their names, there does not appear to be an angel named Castiel in any easily referenced original text. The person to thank for his creation may not be a god of heaven and earth, but of television, in the form of Eric Kripke.
