It's at least an interesting turnabout that a character originally intended as a stock stereotypical threat-- in this case, that of a nasty Commie spy-- should eventually become one of Marvel Comics' most respected heroines.
When the Black Widow first appears in TALES OF SUSPENSE #52, her only superpower was her mysterioso hotness.
Garbed in this Natasha Fatale getup she unsurprisingly pulls the wool over Tony Stark not once but twice, but both times she's ultimately thwarted by Iron Man.
Since Lee and/or one of his collaborators had given her a super-person sort of name, though-- one that even suggested a "Black Widow" who'd been published by Marvel's ancestor Timely in the 1940s-- it probably posed no great leap of logic for Stan and Co. to rethink her as a costumed supervillain with artificially-created spider-powers. Strangely, though it wouldn't be unusual to think of a former spy as possessing martial arts abilities, during the 1960s the new Black Widow was never seen dishing out kicks or karate chops, depending almost entirely on her weapons-system, her "widow's bite" wrist-zapper.
In AMAZING SPIDER-MAN #86 (dated July 1970), her costume was remodeled into its best-known version-- a slick one-piece black leotard-- and she became a practitioner of extraordinary martial arts. The SPIDER-MAN guest-appearance was co-ordinated as a lead-in to her series in AMAZING ADVENTURES, but though that series proved short-lived, the Widow continued to get regular exposure in Marvel Comics through her co-starring appearances in DAREDEVIL and her eventual (though much-delayed) membership in THE AVENGERS.