Dr. Rao is a world-renowned geneticist from India who developed a serum (later called "Hope") which could "cure" mutants, turning them into normal humans.
Hundreds of mutants immediately signed up for the procedure at Benetech (the corporate backer of her research). One of the first was a little girl Tildie that was being kept under her supervision. The X-Men debated the merits of the cure and the significance of labeling the mutant condition a disease. The chance at shedding his "beastly" appearance and avoiding any further secondary mutations held significant appeal for Beast and he considered taking the serum.
It was later revealed that Rao had been working for the alien Ord of the Breakworld who also had in his custody Colossus who was, at that time, thought to be dead. The X-Men defeated Ord and Benetech, and Ord was delivered into the hands of S.H.I.E.L.D.. Dr. Rao's work was destroyed by Wolverine, leaving Hank with the last sample of "Hope".
Rao later joined the X-Club, a group of scientists gathered by Hank and Warren Worthington to assist in solving how to reverse the effects of M-Day.