LOS ANGELES – When Ursula Andress emerged from the sea, curves glistening, with a dagger strapped to her bikini in 1962's "Dr. No," she made the Bond girl an instant icon.

Always glamorous and sophisticated, yet uniquely susceptible to James Bond's flirtations, the Bond girl over the years has become as compelling as Agent 007 himself – and not just for the way she fills out a swimsuit.

"Initially, Bond girls were part of the aesthetic of the series. They had more transient roles," said Karen Tongson, a professor of English and Gender Studies at the University of Southern California. "Especially in the last 15 to 20 years, there's been a marked shift in their greater involvement in the action of the story line and also the motivation for Bond, especially Daniel Craig's Bond."

The greatest change in women's position in the Bond saga, Tongson notes, is that the agent's boss, M, is a woman.

"The sense that the higher power that Bond responds to is this dignified woman played by Dame Judi Dench suggests that the relationships he has with these other (female) figures are not just fleeting casual sexual trysts, but far more complex," she said.

Who qualifies as a Bond girl has also changed over the years, as the blue-eyed, buxom blonde has given way to more diverse leading ladies, including Michelle Yeoh ("Tomorrow Never Dies") and Halle Berry ("Die Another Day"). Modern Bond girls also present a more formidable challenge to the suave secret agent.

"They reflect some of the shifts in the post-feminist perspective: Women who use their presentation and their wiles to outsmart Bond," Tongson said.

One thing that hasn't changed? Whatever their role, Bond girls still must be inarguably beautiful.