In order to attract audiences at the time, Millar worked with artist Bryan Hitch to completely redesign Nick Fury to look almost exactly like Samuel L. Jackson.
Understandably, Jackson almost took legal action, until he and Marvel made a deal instead: if Nick Fury were to ever appear in a Marvel movie, Samuel L. Jackson would be offered the part.
Unfortunately for Millar, Samuel L. Jackson was an occasional comic reader, so this blatant change to Nick Fury did not go unnoticed by the Pulp Fiction star.
As it turns out, however, Samuel L. Jackson and his inclusion in the MCU is pretty much a legal obligation by Marvel due to a copyright infringement from 2001.