When Wal-Mart announced that Doug McMillon would become the retailer's fifth ever CEO starting in February, only the timing was a surprise. McMillon, 47, has steadily risen up the company's ranks and has long been pegged as a possible successor.

But unlike many CEOs of massively profitable companies, McMillon started out at the very bottom of the company he's going to lead. And not as an intern or management trainee. The Arkansas native spent two summers as a teenager unloading trucks at a Wal-Mart distribution center.

Here's a look at McMillon's journey from Wal-Mart's loading dock to its next CEO.

After attending college at the University of Arkansas in Fayetteville, McMillon returned to the company in 1990, working in a store in Tulsa, Okla., as a buyer trainee in the athletic department while getting his MBA at the University of Tulsa. A year later, he made the move to its headquarters in Bentonville, Ark.

From there came a series of promotions, aided by the fact that McMillon is by all accounts an extremely affable, charming, and engaging presence, to the point, according to the Financial Times, that he tended to outshine outgoing CEO Mike Duke whenever the pair appeared together.

He's also reportedly close with the Walton family, who are still massive shareholders. Rob Walton, the son of founder Sam Walton, is the company's chairman.

Over the course of McMillon's years at the company, he's worked throughout its U.S. operations. According to Bloomberg Businessweek, he's been a buyer for food, apparel, and crafts and a divisional merchandise manager for home furnishing and infants and toddlers. He worked as a general merchandise manager at Sam's Club (Wal-Mart's wholesale store) and climbed to a Senior VP at Wal-Mart overseeing toys, electronics, sporting goods, and more.

In 2006, he got his first truly high-profile job in the company, as CEO of Sam's Club. According to The Wall Street Journal, that's where he made his reputation by focusing on small-business owners and the sorts of items that could help it better compete with its larger rival in the space, Costco.

Three years later, in a further sign that he was a possible future CEO, he took over the store's absolutely vital international operations from Duke. International stores represent only about a quarter of Wal-Mart's business. While the company is nearly ubiquitous in the U.S., its international business is the future, necessary for the company's continued growth.

Under McMillon, the company brought its "everyday low prices" mantra to the rest of the world and grew international sales to 29% of the company's total.

That's likely the reason that McMillon was elevated over the other potential successor, Bill Simon, who leads the company's massive but stagnant U.S. operations.

McMillon has a big job to do. He has to figure out a way to keep Wal-Mart strong at home against competition from e-tailers like Amazon and traditional retailers like Target. He'll also need to push international growth and move into markets like India and China where its business model may not even work. And he has to figure out an increasingly digital future for a company whose success is built on a ruthlessly efficient supply chain, razor thin profit margins, and the location of its stores.

McMillon's managed to rise from loading dock worker to Wal-Mart CEO in three decades. We'll be watching what the new leader of the world's largest retail company does next.