#3 The Shield (2014)
The Shield brought together three men from NXT in Roman Reigns, Dean Ambrose and Seth Rollins.
The trio debuted toward the end of CM Punk's title defence versus John Cena and Ryback at Survivor Series 2012. The threesome, destroyed Punk's opponents, enabling him to walk away still WWE Champion.
From there, The Shield defeated everybody on the roster in matches and outside of the ring. They were credited with sidelining The Rock and The Undertaker for significant periods of time.
"The hounds of justice" however would later become "guns for hire" by The Authority. It was this role that disagreed with them and they grew increasingly tired of the antics of Kane and Triple H in particular.
It was the segment that took place on March 17, 2014, wherein The Shield officially completed their face turn when they turned on The Authority.
It was a hugely entertaining moment which later led to Seth Rollins once again siding with The Authority and turning heel on his Shield "brothers"; a development which turned all three into bonafide main-eventers.
No doubt, the most important face turn of the current era.