We rarely repeat names on our Power Players list from year to year, but an exception was necessary for Kristin Lemkau. The chief marketing officer of JPMorgan Chase is once again making waves that the ad industry can't ignore.

After rising to the top marketing role at Chase three years ago, Lemkau has championed industry change, arguing for price transparency among media agencies and initiating an audit of Chase's shops. The Boston-born executive also took on the issue of brand safety following the appearance of Chase ads on fake news sites, including one promoting "Hillary 4 Prison" earlier this year. In a bold experiment, Lemkau pared the sites where Chase advertises to 5,000 from 400,000—and found little change in the cost of impressions or the visibility of the ads.

"We were just focused on reach," says Lemkau, who had brought programmatic in-house to save costs. "Fewer is better—we're less concerned about low CPM [cost per thousand impressions] than in making sure we're in a place appropriate for our brand." (Chase's list of sites has gradually increased again but remains far smaller than before.) The financial services giant still hasn't resumed advertising on YouTube, where its ads had appeared next to offensive content, though Lemkau says the company is working with Google on the issue.

Shaking up existing models is par for the course for Lemkau. She's added edginess to Chase's consumer-facing campaigns, recently partnering with comedian James Corden to promote the brand's Sapphire Reserve card in a campaign with Droga5. And she's focusing on content partnerships such as a jointly branded newsletter with news site Ozy and a personal finance video series with Group Nine Media to further engage customers.

Lemkau personifies the changing role of CMO, which she described at a recent Association of National Advertisers Masters of Marketing event as many things: "a data scientist, a psychologist, a media planner, a technologist, a media buyer and a revenue producer."

On a personal level, Lemkau is also applying her marketing skill set to promote tighter gun safety laws. Following the Las Vegas mass shooting—the nation's deadliest—in September, she was one of the first of dozens of CMOs to sign a petition calling for universal background checks of gun buyers and for safer firearms storage.

"There's awareness that people who understand how to shape a narrative can be influential on an issue that may be full of misperceptions," Lemkau says, adding that she signed as an individual, not as CMO of Chase.