Occasionally (albeit incorrectly) thought to be the weapon used by Cain to slay his brother Abel. A quick look at Genesis 4 specifies no murder weapon, merely that Cain

rose up against Abel his brother, and slew him.

The jawbone of an ass does actually show up as a weapon in Judges 15, employed by Samson to slay a thousand men of unspecified nationality, presumably Philistines from the passages before.