Names this 'character' is known by both in fandom and canon:
- The Demon (all Winchesters refer to it thus in Season 1)
- The Yellow-Eyed Demon (Dean refers to it thus in Season 2)
- Celine Demon (a nickname used by the fans. See below for an etymology of this nickname)
- In a draft script for 2.02, Dean refers to it as the Big Bad.
- The Demon attacks families on the night the baby is exactly 6 months old. (Jess is the exception to this rule - Sam is 22 & 6 months old.)
- A week prior to the attack, the geographical area has cattle deaths, electrical storms and temperature fluctuations.
- It makes clocks stop, and electical devices go haywire.
- It is impervious to Holy Water
- Following what appears to be a surge of activity around the time Mary died (Max's mother was also killed around this time), the Demon was dormant until late 2005.
- It has yellow eyes (iris and pupil).
- It possesses human hosts, but can exist in a disembodied form also.
- Impervious to the salt barrier.
- It is vulnerable to the Colt.
The Demon's Children
- Possess human hosts, are able to animate the human body they are possessing even if the body sustains mortal injury.
- Eyes turn entirely black during possession, though this can seemingly be turned on and off.
- They are impervious to hallowed ground ("that may work in the minor league, but not with me" - Meg, Salvation), but not to Holy Water.
- They can be exorcised and thus destroyed.
- Possession can occur by physical contact.
- Restricted by the salt barrier.
- Vulnerable to the Colt.
'Croatoan' and "demonic germ warfare"
In 2.09 Croatoan, Sam says, "I've been pawing through Dad's journal, I found something about the Roanoke Colony. Dad always had a theory about 'Croatoan'. He thought it was a demon's name, sometimes known as 'Deva', sometimes 'Resheph', a demon of plague and pestilence."
Considering how the episode ends - with Duane Tanner communicating with an entity much as Meg did in Season 1, saying that "The Winchester boy is immune" (to the virus) - and considering Sam's vision that lead them in the first place, it's reasonable to assume that this 'demon virus' is linked in with The Demon somehow.
Sam's pronunciation of the name ("Deeva") suggests a relationship to Hinduism wherein a "deva" is used to refer to demi-deities.
Monstropedia's discussion of demons in Hinduism traces the etymology of the term 'deva' to suggest its roots in both 'good' and 'evil' deities, and furthermore links the term to 'Asura', relating back to Iranian Zoroastrianism, a religion that crops up frequently in Supernatural's mythology:
- Originally, the word Asura ... meant any supernatural spirit—good or bad. Hence even some of the devas (demigods)... have the epithet of Asura. In fact, since the /s/ of the Indic linguistic branch is cognate with the /h/ of the Early Iranian languages, the word Asura, representing a category of celestial beings, became the word Ahura (Mazda), the Supreme God of the monotheistic Zoroastrians. But very soon, among the Indo-Aryans, Asura came to exclusively mean any of a race of anthromorphic but hideous demons.
Indian Myth and Legend by Donald A. Mackenzie further links the etymology to the nature of 'deva':
- In the old Persian language, which, like Greek, places "h" before a vowel where "s" is used in Sanskrit, Ahura (= Asura) signifies "god". The Zoroastrian chief god is called Ahura-Mazda, "the wise Lord", as Varuna is addressed in early Rigvedic hymns, "wise Asura and King", and "the all-knowing Asura who established the heavens and fixed the limits of the earth". On the other hand "daeva" in the Iranian dialect, which is cognate with Sanskrit "deva", "god", came to mean "demon". "Asura" is derived from the root "asu", which signifies "the air of life", and "deva" from "div", "to shine", or "deiwo", "heavenly".
Wikipedia's entry on Divs suggests that they are more ambiguous than evil, however (or rather, that 'demons' aren't necessarily considered evil in Zoroastrianism, a point Monstropedia makes about Devas in Hinduism also). Wikipedia also translates 'div' directly as 'demon'.
According to Wikipedia,
- Resheph was a Semitic god of plague and war. He bore the head of a gazelle on his forehead and was an important member of the pantheon of Ugarit though not mentioned in Ugaritic mythological texts.
This is not the first time Mesopotamianism has cropped up in speculation around Supernatural's mytharc; there's a theory that Dean's Amulet is a Mesopotamian figure.
Etymology of the "Celine Demon" nickname
The term Celine Demon has been coined on the TWOP boards on September 14th, 2005, in a discussion after the airing of the 1.01 Pilot (episode) and means the demon, who killed the Winchester brothers' mother Mary Winchester.
It derived from a misreading of the words Ceiling Demon as Celine Dion (Canadian popsinger) by TWOP-user thinkcwik. The singer's name and the nickname for the demon were meshed and the new term stuck.