It inspired a lot of films as well. Michael Mann's Collateral is an example, as well as Jarmusch's Ghost Dog: The Way of the Samurai which I have yet to see. Luc Besson's Leon (The Professional) is another, which substitutes Costello's bird with a plant. Besson also wrote The Transporter, which takes some of the aspects of Jef Costello, primarily the strict code of professionalism.