#4 ECW invades WWE (the first time)
If you're wondering why WWE and Vince McMahon would take a chance on featuring a different wrestling promotion on their show, there's a very good reason for it. Because it worked before - and less than a year earlier.
The 1995 King of the Ring took place in Philadelphia, PA, home to Extreme Championship Wrestling. During the main event - the tournament final between Mabel and Savio Vega - fans in the audience began to chant "E-C-Dub" loudly and Vince McMahon took notice.
Unlike its competition in Atlanta, ECW didn't really pose a significant threat to WWE. However, it was also expanding and was confident in presenting its very first Pay-Per-View event, ECW Barely Legal, in 1997. McMahon, knowing a win-win when he sees one, brought Extreme Championship Wrestling to the WWE audience - and gave his company the "cool factor" it was clearly missing.
Things kicked off in September 1996, at In Your House: Mind Games. Once again in Philadelphia, representatives from ECW (The Sandman, Tommy Dreamer, and Paul Heyman) sat at ringside. During a match between Bradshaw (aka JBL) and Savio Vega, Sandman spat beer right into Vega's face. According to Dreamer, Bradshaw wasn't made aware of the planned attack and had to be restrained by Vega from attacking the ECW trio.
Two weeks later, ECW arrived at the Manhattan Center in New York City for an episode of RAW. ECW matches were held, Paul Heyman was at commentary (even offering Vince McMahon an announcing job with his promotion if "this WWF thing [didn't] work out"), and promoted their upcoming debut pay-per-view.
ECW stars arrived on WWE programming over the coming weeks, and most were loyal to their extreme brand. All but Rob Van Dam, who decided to turn on the company, sided with ECW's main antagonist during the angle, Jerry "The King" Lawler; and would dub himself "Mr. Monday Night."
The entire feud came to a head at ECW's Wrestlepalooza 1997 that June. Following a Loser Leaves Town match that saw Dreamer send his long-time rival Raven packing to WCW, Van Dam and his cohort, Sabu, came to the ring to attack the Innovator of Violence. Joining them in the ring was none other than Jerry "The King" Lawler.
As we'll see, while this was the end of the "original" ECW invasion, it would hardly be the last time the hardcore brand and WWE collided.