If the $42.3 billion spent online this past holiday season has taught retailers anything, it’s that capturing customers—and their dollars—online is crucial.

But online is a big place. And mobile, which can seem like an entirely different universe, looms ever larger. So where to even start if you haven’t yet…started? And who should lead the charge?

The modern day merchant must have an intimate understanding of the importance of online and mobile commerce, access to a vast array of customer data, and a strategy for transforming this analytical data into winning online experiences.

In all cases, the goal is to attract and retain both new and returning customers. Whether online novices or experts, business leaders crave insight on how to accomplish this. The question is: who inside the company can embody these traits and help the CEO rule the roost? That responsibility should belong to the chief marketing officer.

A CMO should be somebody who uniquely understands marketing, merchandising, data, analytics and web design, and who can also maintain a creative, innovative organizational structure. IT tends to lean too heavily toward data for data’s sake, while Sales too often relies on revenue and relationships.

Placing the CMO in charge allows for the best of both worlds. Armed with the science of data analysis and the art of consumer engagement, the CMO is well positioned to emulate merchant princes of old and join the ranks of retail royalty. A good CMO can nurture a culture of testing, measuring and learning instead of depending on guesswork and subjectivity, as well as reach out to those on the front lines of customer interactions to figure out what those customers want. The ambitious CMO knows that their company site must be more engaging than the competitions’, as well as a place that customers trust, valuing the available products, services and information on offer. It also needs to be a reliable gateway to actions that grow sales beyond the initial purchase, such as cross-selling and upselling.

What’s the best way to make all this happen? One word: data.

Data is crucial to online retail. It comes in many different forms, the main type being the individual behaviors of current site visitors: which search term or webpage brought them over, what time of day and day of the week they’re most likely to stop by, what recent purchases they’ve already made onsite, what pages they visit and what product categories most interest them. All this pertinent info helps define what the “best content” is for each specific viewer. Other types include customer relationship management (CRM) data and social media data.

The aspiring CMO must then use this accumulated data to gain perspective on what customers want; analytical optimization and personalization tools will aid in this quest. Segmentation sifts through the data to find discrete groups of people with similar traits and/or interests, who can then be targeted and tested with relevant content based on site activity. Product recommendations and other offers are then provided based on what the various groups are most likely to purchase.

Product information tools give customers a deeper understanding of the product at hand—a 360-degree view of an article of clothing, or a close-up of various types of textured materials. User-generated content, like ratings, reviews or social media feedback, also aids and influences purchasing decisions. The savvy CMO uses all these methods to strike the delicate balance between intuition and analysis.