After the Attitude Era concluded, WWE transitioned towards the Ruthless Aggression Era in 2002. With Stone Cold Steve Austin, Hulk Hogan and The Rock eventually departing, WWE turned towards its new wave of superstars to carry the torch. This included John Cena, Batista, Eddie Guerrero, Randy Orton and Edge.

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During the Ruthless Aggression Era - which lasted up until 2008 - we saw some top-notch and Hall of Fame-caliber heels emerge. These superstars helped put the new generation of babyfaces over for good. But on the flip side, there were numerous superstars pushed as big-time heels that never fully lived up to their hype.

10 BEST: JBL

After going through several gimmick changes at the mid-card level, John Bradshaw Layfield finally got a major push in 2004, when he entered a program with WWE Champion Eddie Guerrero. JBL's big mouth, obnoxious attitude and knack for showing off his wealth made the Texan an excellent heel on the SmackDown roster. It also helped in that he always found sneaky and clever ways to retain his WWE Championship over big-named stars like Guerrero, The Undertaker and Big Show.

His WWE Championship run finally ended after 280 days, when JBL lost to John Cena at WrestleMania 21. That marked a career-defining moment for Cena, who became the new face of WWE. JBL deserves plenty of credit for helping Cena get over as a main event star, too.

9 WORST: Simon Dean

Best known for his work as part of the "Blue World Order" in ECW, Mike Bucci joined WWE in 2002, and he was repackaged as "Simon Dean," a fitness guru who continually endorsed his Simon System to help others lose weight.

This was clearly done in an effort to provide laughter for fans, but WWE may have missed the memo: The '90s were long gone; this was no longer the era where Vince McMahon could have more cheesy characters (The Goon, Repo Man, Isaac Yankem, and others). WWE could have done so much better with Bucci.

8 BEST: Randy Orton

Orton spent over a year with the Evolution stable, alongside Triple H, Ric Flair and Batista. Though Orton quickly got over as a babyface when he became a 24-year-old World Heavyweight Champion (thus leading to a feud with Triple H), the Viper was simply at his best when he portrayed a heel.

"The Legend Killer" took part in many memorable feuds with some of WWE's top faces, including John Cena, Undertaker and D-Generation X. Orton's vicious and merciless persona, along with his top-notch microphone skills, made him can't-miss television in the Ruthless Aggression Era. Over a decade later, and Orton hasn't changed a bit. He's as good as ever.

7 WORST: Vladimir Kozlov

It's hard to keep track of how many anti-American superstars Vince McMahon has tried pushing over the years. Only a handful of them really got over, but Vladimir Kozlov wasn't one of them.

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Kozlov's aggressive and intimidating appearance made him into a quickly-disliked heel by fans. That much worked. However, he simply wasn't able to offer a whole lot in the ring, and he was named the most overrated wrestler of the year by the Wrestling Observer Newsletter in 2008.

6 BEST: Kane

Kane's feud with The Undertaker during the Attitude Era made him one of the company's most valuable heel figures. He didn't lose any of that magic in the Ruthless Aggression Era, continuing his ways as a feared and intimidating bad guy.

For starters, he "buried" The Undertaker during the latter's match against Vince McMahon at Survivor Series 2003. He ruined Matt Hardy's storyline proposal to Lita, much to the chagrin of WWE fans. Kane also viciously assaulted many fan favorites like Hardy and Shane McMahon, among others. But his ruthless attitude made The Big Red Machine one of WWE's elite bad guys in the 2000s.

5 WORST: Heidenreich

It's safe to say that Heidenreich's character and persona wouldn't work in today's WWE. The company placed him in some disturbing and uncomfortable storylines and segments, thus ruining his chance to be one of WWE's all-time great heels. Heidenreich had the look and size to be a true main event talent. But WWE's plan to make him a terrorizing "psychopath" didn't go as planned.

He worked better as a babyface, especially after teaming with Road Warrior Animal (the two won the WWE Tag Team Championships together on one occasion). Even the legendary Paul Heyman wasn't able to do much to help Heidenreich really get over. It didn't take long for the company to scrap the idea of pushing him as a main event talent.

4 BEST: Triple H

Triple H bounced around from heel to babyface during the Ruthless Aggression Era, and he shined in both roles. One can only wonder what the Ruthless Aggression Era would have gone if he wasn't around as one of the top bad guys. His tenure as the leader of Evolution was one of the defining storylines of the 2000s. They picked on all the popular faces, including Goldberg, Chris Jericho and eventually Randy Orton.

RELATED:10 Worst Things Triple H Ever Did (In Wrestling)

We also can't forget the time where Triple H betrayed Shawn Michaels and attacked him after teasing a DX reunion. And finally, if it weren't for his heel persona, perhaps Orton and Batista wouldn't have gotten over as heels. Triple H did his part in paving the way for the next wave of elite babyfaces.

3 WORST: Great Khali

The Great Khali was given a major push right away when he debuted in 2006, entering a program with The Undertaker. Despite having an extremely limited skill set in the ring, The Great Khali quickly became one of Vince McMahon's personal favorites. Sure, he had the size and physique that could have made him a main event heel. But with only a handful of moves in his playbook, Great Khali couldn't really get over as one of WWE's top bad guys.

Even feuds with Undertaker and Batista - along with a run as World Heavyweight Champion - weren't enough to push him. Great Khali simply worked better as a lovable babyface and gentle giant near the end of his time in WWE.

2 BEST: Edge

Edge spent the early years of his WWE career in the tag team division with real-life friend Christian and Rey Mysterio. But near the end of 2004, WWE made the decision to turn him heel, and he won the Money in the Bank ladder match at WrestleMania 21. Less than a year later, he cashed in his contract after John Cena defended his WWE Championship in an Elimination Chamber match at New Year's Revolution 2006.

The Rated-R Superstar became the new WWE Champion, and his heel persona would grow from there. Edge's real-life relationship with Lita (she was previously with Matt Hardy) drew more hatred upon the Ultimate Opportunist. He had everything you wanted in a heel. The elite in-ring work, the top-tier mic skills, the ability to pull off sneaky victories as well as a habit of costing main babyfaces their championship opportunities. It's no wonder WWE kept Edge as a heel for five whole years.

1 WORST: Spirit Squad

Yes, there are five superstars in this entry, but we're going to count them as one.

This group had Nicky (now Dolph Ziggler), Kenny, Mitch, Johnny and Mikey. Vince McMahon gave them a big push immediately, as they assisted him and Shane in going up against D-Generation X.

But whole gimmick was cheesy, and quite frankly, irritating. But you knew Vince saw something special in this group together. As it turns out, that "something special" apparently meant getting humiliated and dominated by DX time and time again.

NEXT: 10 Things We Want To See On The Road To WrestleMania 36