Onomatopoeia first appeared in Green Arrow Vol 3 #12 in 2002 and was created by Kevin Smith and Phil Hester. Onomatopoeia is an enemy of the Green Arrow and hitman who imitates sounds that he hears, such as explosions.
A graduate student at Gotham University discovers a long-buried secret about his lineage and sets out to fulfill the bidding of a nefarious religious order; putting him in the crosshairs of Batman and his enemies.