Mystique

Mystique is a major villain from the X-Men comics and media,a somewhat treacherous ally of Magnetowho has worked as part of the Brotherhood but has also taken over - being capable of even more radical thinking than Magneto at times.

She is one of the X-Men's most deceptive and cunning opponents, happy to do what it takes to get the upper-hand and ensure mutant supremecy - this ruthlessness has been displayed when she attempted to kill her own adoptive daughter (Rogue) and and son nightcrawler on numerous occassions.

Mystique is also quite happy to switch sides if it is in her interests and this combined with her formidable shapeshifting abilities serves to make her a very dangerous opponent.

Origin
In the movie X-Men, it was revealed that Mystique's own family tried to kill her for being a mutant. Later, she joined Magneto and became his trusted right-hand.

In the comic books however Mystique's past is much more mysterious, her exact age is never revealed but some stories have her around in the late 20th century and during her travels would have a relationship with Sabertooth, ultimately producing Graydon Creed - oddly enough despite his origins Graydon would grow to be a human rather than a mutant and indeed would be one of the X-Men's greatest enemies as the leader of the anti-mutant organisation Friends of Humanity - at any rate Mystique soon broke up with Sabertooth and would continue on her tour of the world, according to some stories she would mother Nightcrawler at some point during these travels to the demonic mutant known as Azazel but she would abandon this child as well.

Ultimately Mystique would gain a final child via adopting Rogue and settle into a criminal career as part of the Brotherhood, where she would grow to be one of the X-Men's most hated and reoccuring foes - the innumerable schemes she and her followers committed would be too vast to summarise here and continues to grow as her increasingly complex story continues to unravel..

Powers and Abilities
Mystique has the ability to shape-shift into anyone she chooses, even those of the opposite gender and is well versed in all manner of both armed and unarmed combat.

These powers combined serve to make her a stealthy opponent capable of tricking many, however it is not as effective against Wolverine, as she can not disguise her scent without aid - she also suffers from the limit that she can not shapeshift into non-humanoid forms.

In the comic book canon only she displays the additional powers of regeneration and immunity to age, said to be connected to her ability to shapeshift.