A hell demon that was banished from hell for distrupting the apocalypse.
Previously known as Knives, the X was added by Diablo as a mark for his betrayal and so banishing him forever from the demon race.
XKnives brought uppon to cyclone of powers the rage of fire and blade named "Avatar of Hatred" and tilted the balance, destroying the gates to the mortal world, for all eternity.
XKnives the combination of an X ( unkown, unpredictable, l337) and Knives, that are simply and definetly sharper then you are and therefor cooler.
XKnives killed you coz he's a Ninja!