Lilith

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Name	Lilith
Actor
Dates
Location	Originally - Hell, since 2.22 - "the west" of the USA
Occupation	High-tier Demon
Episode(s)	3.12 Jus in Bello

Lilith is Sam's demonic rival.

The demon Lilith is one of the most infamous in demonology.

In Supernatural, she is first referred to - though not by name - in 3.09 Malleus Maleficarum when Ruby warns him of a rival "in the west".

In 3.12, Ruby accounts the demon hoard to Lilith. At the end of the episode Lilith shows up looking for Sam & Dean before destroying the sheriff's office (and its occupants).