a representation of Death, as in literature or the Bible.
Before X Was X: The Dark Horse Story Of The 24th LetterSince its inception, the letter X has struggled to establish its own identity, so it may be no coincidence that X is commonly used to represent the unknown in both language and mathematics. But, how was it created?
Origin of Pale Horse
after the Biblical pale horse on which Death rides, Rev. 6:8
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019