The Nexus: Although they started out with eight, it's been whittled down to a group that fits this pretty well.
Big Bad: Wade Barrett of course, he's the leader and the one who takes on the main eventers and gets the WWE title shots.
The Dragon: Justin Gabriel was the second-last eliminated in the SummerSlam tag, and is the only one other than Barrett who routinely faces guys like John Cena and Randy Orton one on one. His 450 Splash is also the Nexus' strongest weapon.
The Evil Genius: David Otunga, who graduated Harvard and is the most well-spoken. When the Nexus first showed up on Raw, it was Otunga who handled the negotiations with management. Also doubles as The Starscream.
The Brute: Michael Tarver, who behaves like an attack dog, often delivering the most vicious beatings during a Nexus attack, and who can knock anyone out in 1.9 seconds. Skip Sheffield fit this trope like a glove before his injury.
Sixth Ranger Traitor: John Cena, who lost a recent match with Wade Barrett, forcing him to join the Nexus. Ultimately a sympathetic example, as he's following Barrett's orders only because the GM of Raw threatened to fire him if he didn't. Daniel Bryan is also a good example of this trope in action.