As the girlfriend of Reed Richards and sister of Johnny Storm, she was instrumental in persuading pilot Ben Grimm in joining them on a dangerous space mission, which got them massively exposed to cosmic radiation. As a result, she gained the ability to become invisible at will. Unfortunately, this power alone proved to be of relatively little use in their missions, especially compared to the more aggressive ones of the rest of the group. Fortunately, creators Stan Lee and Jack Kirby realized this and gave Susan the ability to project telekinetic forcefields which could also make other things invisible.
However for her abilities, Susan served primarily as an helpmeet and adjunct to Reed and the comics tended to treat her in a condencing matter. This changed when John Byrne began his celebrated run on the title. Under his authorship, Susan became much more confident and assertive in her own abilities which themselves became more versatile and impressive. Eventually, she came to be recognized as the most powerful member of the team which served her well, including as leader.