Susan Storm, better known to the public as the Invisible Woman, is the girlfriend and later wife of Mr. Fantastic as well as the sister of the Human Torch - she is the more down-to-earth of the group and often acts a bit like a mother figure, keeping the others from causing too much trouble with their bickering and also trying to get Reed to stop being quite so "nerdy" and enjoy life a little. She is fiercely protective of her friends and views the Fantastic Four as her family, any villain foolish enough to provoke her quickly learns this fact - and Susan is no push over, being one of the most powerful members of the team.
As her name implies, the Invisible Woman can turn herself and others invisible at will - she can also form a number of force-fields around herself and others that can be used for defense or as a means of attack, or even both. She is also a fairly experienced hand to hand combatant with such notable mentors as She-Hulk and Iron Fist, and is a capable leader when she has to be.