Emma Frost has worn many hats in the history of the X-Men. Sometimes she's good guy, sometimes she's not, but she's always interesting. Not only does she have the raw power to be classified as an Omega Level telepath, she has the skill and training to wield that power better than almost anyone on the planet. She also has a secondary mutation that allows her to change into a diamond form, making her super strong and nearly invulnerable to pretty much anything. Emma is essentially a combination of Professor X and Colossus, which makes her an incredible ally and a devastating foe.
10 VILLAIN: The White Queen
For many X-Men fans, they were introduced to Emma Frost as the White Queen of the Hellfire Club. After finding out that the humans running the club were planning to destroy all mutants, Frost joined forces with another powerful mutant named Sebastian Shaw to take over the Club. Once in charge, they used the power and influence they acquired in an attempt to rule the world. This put Emma and the Hellfire Club in the position to fight the X-Men on several occasions. Her considerable resources combined with her mutant powers made her one of the X-Men's greatest enemies.
9 HERO: Re-Building Xavier's School
During an incident involving the mutant Xorn, Xavier's school was destroyed, an event that also resulted in the death of Jean Grey. Despite the fact that Emma and Jean were in competition for the affections of Scott Summers, they had each other's backs when it counted. Jean's loss was felt by everyone, which was only amplified by the destruction of the school.
Of all the people involved in the school, it was Emma Frost who pushed Scott the hardest to rebuild and restart Xavier's vision, which they did. Jean, who was in the weird Phoenix afterlife known as the White Hot Room, also had a say in the matter.
8 VILLAIN: The Hellions
The New Mutants were the X-Men's answer to the Teen Titans, a group of teenage mutant heroes preparing to fight for the future of their kind. On behalf of the Hellfire Club, Emma Frost created an opposing team called the Hellions. Her recruitment efforts constantly put her at odds with the X-Men as they fought over the next generation of mutants. At one point, she even used her vast telepathic powers to convince Kitty Pryde's parents to transfer her to the Massachusetts Academy, which the White Queen was headmistress of. Emma had no compunctions about using her powers to her advantage in situations like this.
7 HERO: Generation X
While leading the Hellions, Emma was attacked by a time travelling mutant name Fiztroy who put her in a coma. When she woke up, she found that Fitzroy had killed the vast majority of the Hellions. It was one of the most devastating moments of her life, one that set her on a new path.
Emma gave the Massachusetts Academy to Professor X who made it an extension of his own school. Once she recovered from her ordeal, Emma teamed up with Banshee to help train a new group of X-Men called Generation X. She took to this new role brilliantly until an incident that resulted in the death of a student drove a wedge between her and her new team.
6 VILLAIN: Becoming Storm
The first day of school is special day. Well, unless you're Kitty Pryde and you've been transferred from the Xavier School for Gifted Youngsters to the Massachusetts Academy. Always the supportive friend and mentor, Storm took Kitty to the Academy and dropped her off. Emma Frost seized the opportunity to switch bodies with Storm. She used her new body to help Shaw, and a group of brand new Sentinels, attack the X-Men. While Storm was able to use Emma's own powers to switch back and help stop the attack, it was still dangerous move on Emma's part.
5 HERO: Fighting The Skrulls
During Secret Invasion, the Skrulls set up a telepathy blocking wall in San Francisco, the location of the X-Men's new base. With the help of the Stepford Cuckoos, a group sister telepaths, Emma took on the Skrulls only to be apparently killed.
In reality, her mind was continuing to take on the Skrulls' telepathic team single handedly, eventually coming out on top. Frost broke through their psychic defenses and demolished the blockade. Once again, Emma proved why she is considered one of the most powerful telepaths on Earth.
4 VILLAIN: Manipulating Warpath
Emma Frost is never above using every angle available to her advantage, including personal loss. Desperately searching for someone to lead her Hellions, she finally found a Native American mutant who fans today know by the name Warpath. In those days, he fought under the name Thunderbird in honor of his brother, a mutant who fell in battle as part of the X-Men. Emma played on his bitterness towards Professor X to bring him into the Hellions and lead them. Warpath would eventually leave that life behind and join X-Force under Cable's leadership.
3 HERO: Founding Utopia
The X-Men, and mutants in general, have struggled to find a place to call home. Safety is a difficult thing for mutants to find when the whole world hates you. Almost every attempt to create a home has resulted in destruction but Emma helped take a hell of a shot at building something nice. She played a key role in creating Utopia, the X-Men's island base off the coast of San Francisco.
It started its life as Asteroid M, Magneto's space base. After it crashed to Earth, X-Club used it as the basis for Utopia. Emma was a big part of not only founding it but defending it from the likes of Norman Osborn.
2 VILLAIN: Messing With Magneto's Head
At the same point Emma was the headmistress of the Massachusetts Academy, Magneto was the headmaster of Xavier's school. After an incident with the Beyonder, specifically being killed and recreated by him, The New Mutants were shadows of their former selves. Uncharacteristically, Frost appeared to Magneto and offered to help him with his students. She also used the opportunity to have one of her Hellions use his abilities to influence Magento to transfer most of his students to the Massachusetts Academy, an act which was far more on brand for her.
1 HERO: Screwing With Osborn
One of the darkest times in Marvel's history saw Norman Osborn take control of what was S.H.I.E.L.D. and most of the superhuman activity in the United States. He invited several like minded people to join his Cabal, an evil ruling elite, including Emma Frost. She joined, attempting to us her new position to make sure mutants were treated fairly under Osborn's rule. In addition, he also put Frost in charge of the Dark X-Men. It turns out that Frost was playing Osborn in order to free the mutants he had been capturing. Her betrayal incensed Osborn but even his most powerful minions couldn't defeat the X-Men.