Walmart U.S. Chief Marketing Officer Tony Rogers is moving over to sibling Sam's Club in the newly created role of chief member officer -- a surprise move that takes him from running marketing for the world's biggest retail chain to a club store that's in an underdog battle against Costco.

Rogers says his replacement as Walmart CMO has yet to be named, and he won't move to Sam's until late July, leaving time for a transition.

"When I was in China I worked for [Sam's Club CEO] John Furner, and I was really drawn to him as a leader," Rogers says. "He rang me up recently and said they were going to create this job."

Rogers says he found the post appealing because after 20 years in marketing working on packaged-goods, tech, retail and customer marketing, this will be his first time working with a membership database.

"The other thing, when I look at the Sam's brand as a marketer, I see a lot of untapped potential, kind of how I saw the Walmart brand when I came here 12 or 13 years ago," Rogers says. "But you don't always hear about it because it's part of Walmart."

Rogers comes to a Sam's Club with improving recent results and strong momentum, Rogers says, but also the opportunity to increase a relatively small e-commerce business. Rogers says he relishes playing the underdog for the first time in a while by going up against Costco, which also has lagged Walmart – and far more so Amazon -- on the e-commerce front.

"Walmart tends to be at its best when we have a competitor that focuses us and galvanizes us," he says.

The heaviest annual lifting for a Walmart CMO is done for the year. "We've greenlit all of the holiday advertising on the Walmart side," Rogers says. "It's all in production. The in-store presentation is all in production, so the plans are well under way."

Rogers has made some big changes at Walmart in just two-and-a-half years on the job, including consolidating the Walmart physical stores and e-commerce marketing teams into a single unit distributed across three cities. He also consolidated Walmart agencies under a single Department W banner, led by Publicis Groupe and Saatchi & Saatchi, New York, but including independents such as Mono and Lopez Negrete, along with a new media agency – WPP-backed Haworth – which replaced Mediavest.

Rogers says he won't be tempted to roll out a big national media campaign for Sam's akin to what Walmart does.

Sam's, he says, "Really reminds me of my experience in China where we did a little advertising but not a ton. But the opportunity is more about understanding the customer or member and then translating those things to new services or products."