Though the Valkyrie may be viewed as Marvel Comics' first true powerhouse, Storm is the first one to take on mythic properties in terms of her popularity.
Created by Len Wein and Dave Cockrum for GIANT-SIZED X-MEN #1, Storm was one of several new characters designed for the new "international X-Men," one of Marvel's attempts to diverge from the dominantly WASP-y look of most superhero books. Storm possessed formidable powers, able to conjure up great winds, snowstorms, and lightning. Yet her dominant characterization-- that of being regal, yet without pretension-- may have been the quality that most endeared fans to the character. Her original costume by co-creator Dave Cockrum most coalesces both her queenly bearing and her "child of nature" attitude.
It's interesting to speculate whether or not Storm, or other X-Men, would have become as persuasive had Chris Claremont not taken over the series' writing from Wein. Today it's fashionable to sneer at Claremont's stylistic affections, but his passion for the characters-- particularly in terms of giving X-MEN's female characters their unique charisma-- can't be underrated in assessing the success of the series and its protagonists.