The name of the character Sam is derived from Samhain, the ancient Celtic festival of the dead from which modern-day Halloween is derived. Despite having been portrayed as such in this film and several other works, Samhain is not a deity or other personage of ancient Celtic polytheism; it is only the name of the celebration. However, the idea of being either a deity or other personage dates back to at least the late first century, largely thanks to an Irish bishop named Cormac mac Cuilennàin and his book "Sanas Cormaic" (Irish Gaelic for "Cormac's Narrative"), which had identified Samhain as such.