Cas

Misha Collins plays Cas or is it Cass?

Cas is a nickname for Castiel, first used by Dean in 4.04 Metamorphosis when he says to Sam "Cas said that if I don't stop you, he will." From Season 5 it is commonly used by other characters.

Before its use in canon there were relatively few instances of the use of this diminutive in fandom, and when it did appear it was generally pilloried. Subsequently its use became widespread.

The show's writers spell the nickname "Cass" in scripts source, and it also appears that way in Tie-in novels and the Official Companion books. It is spelled Cass in the Season 7 promo, the promo for the sixth episode of Season 8 and also for the promo of the eighteenth episode of Season 9.

On the Season 4 DVD the English subtitles call him "Cass" and other times it is "Cas."

In fandom, and particularly in fanfiction, it is almost exclusively spelled "Cas." Fans often get annoyed at the show's writers for spelling it differently.

One theory as to the spelling "Cass" is that the writers based Castiel on the angel Cassiel, best known in popular culture from the movies Wings of Desire and the American remake City Of Angels.

However a question from a curious "fan" to Eric Kripke prompted a much simpler answer

:@rthompson1138: why is Castiel’s nickname spelled Cass not Cas? again: for science Eric Kripke: I think “Cass” just looks cooler on the page. And “Cas” might sound like “Caz.” But that’s just my opinion. Now get back to work.

• The angel Cassiel in Judeo-Christian lore.