Shego was once a hero who, alongside her brothers, defended Go City against a number of villains as the superhero group Team Go. Shego eventually left the team for reasons that were never fully specified, but anecdotal evidence suggests there were two primary reasons: a fascination with villainy and irritation with her brothers. At some point, she abandoned her family and their quest for justice for a life as a mercenary-for-hire.
It is unknown what happened with Shego right after leaving her family, but from the beginning of the series Shego has been, for the most part, in the employ of Dr. Drakken as his sidekick and enforcer. It is during this stage of her life in which the series mostly revolves, leading her and Drakken to multiple confrontations against Kim Possible. Throughout the series, Shego is repeatedly defeated by Kim Possible and sent back to jail. She is (as previously mentioned) a formidable fighter and gets the better of Kim Possible a few times, whereupon her successes are usually stopped by Ron (often accidentally), Rufus, or, on occasion, bungling from Drakken or interference from his machinery.
In the second season, one of the most notable events involving Shego was her reunion with her brothers; she had to team up with her rival Kim to retrieve their powers, which had been stolen by an old enemy of hers, Aviarius. This was the first time the show took the time to detail bits of Shego's past.
During the fourth season, Shego’s character went through some development which pointed to the possibility that she may have been growing tired of her established role as a villainous sidekick. She walked out on two separate capers, and on two occasions she actually saved Kim's life. Shego states her reason for doing so is because nobody is allowed to kill Kim, except for her. These incidents, coupled with the events of "Stop Team Go" where she experienced life on the side of good, seemed to point toward a possible redemption of her character. Finally, at the series' end, she and Drakken put their villain issues aside and teamed up with Kim and Ron to save the world from an alien invasion. Because of this, they were greeted as heroes at the end; however, it is unclear whether or not Shego has changed her evil ways.
Shego is an expert in all kinds of fields, with infiltration and sabotage as her specialties. She possesses extensive martial arts training and impressive fitness and agility, rivaling the skills displayed by her nemesis Kim Possible. Her attack is also enhanced by metal claws on her gloves, and on occasion she has used her claw-like fingernails to similar effect. She is often seen filing them.
Shego is endowed with a superpower: the ability to generate green, flame-like bolts of energy in her hands. This energy can be used to heat or melt anything she touches, or fired as a directed energy attack ranging from laser precision to a destructive blast. Originally, Disney described Shego's green flames as being purely concussive in nature, although in later episodes she was shown using her flames to burn or melt things.
These powers were first stated by Disney as being generated by her gloves, making them a weapon rather than a superpower. However, this fact was retroactively changedduring Season 2, when these abilities were revealed to be a true superpower resulting from exposure to the rainbow-hued comet which also empowered her four brothers.
In addition to her energy attack, Shego appears to possess superhuman durability that allows her to survive situations of calamitous destruction that would probably kill other characters. In the Season 3 Finale, So the Drama, she was kicked into a live electrical signal tower, which shocked her and then proceeded to collapse on top of her. She came out of the incident with slightly torn clothes and frazzled hair