#4 Mankind
Like JR, Mankind was an icon of WWE's Attitude Era, but his influences on the edgier product began long before the "Three Faces of Foley". Dude Love and even Cactus Jack made numerous appearances during the late 90s and early 2000s, but it was Mick Foley's 1996 portrayal of Mankind that really presented the WWE with a fresh look on heels.
In April '96, Mankind debuted as a masked, boiler-room dwelling, rat-petting, mutilated freak that was incredibly dark for the time period. In addition to his disturbing appearance, Mankind worked a very physical in-ring style that would later inspire many Attitude Era matches in which brutality was at the forefront.
His Boiler Room Brawl and Buried Alive matches, both against The Undertaker, plus Mind Games classic with Shawn Michaels capped off a stellar year for WWE's newest villain and it set the stage for what was yet to come.