Underlings gave Clark, who has worked at Amazon during almost all of his career, that moniker after he told them that early in his tenure he would hide in the shadows at warehouses seeking to catch lazy workers slacking off who he could fire.

Clark, 47, has come a long way since those days as a lurker. Amazon announced on Friday that he will replace Jeff Wilke, one of the most trusted lieutenants of Amazon founder Jeff Bezos, when he retires early next year. The news surprised some analysts, who thought Wilke might be in line to run the whole company if Bezos ever left. Now it will be Clark, who helped build Amazon’s massive warehouse and delivery network, who is one step away from the top job.

Shares of Amazon, which had been up 78% this year, lost less than 1% on Friday.

“Those of you who have worked with Dave know his incredible passion for serving customers and supporting our employees,” Bezos said in an email to employees announcing the change. “I am excited for him to lead our teams and continue innovating for customers.”

Amazon said no executives were available for an interview on Friday.

Clark grew up in Georgia and Florida and got early exposure to life in the retail business working in his parents’ carpet store (where he liked to drive the forklift) as well as at a Publix Supermarket and a Service Merchandise store during high school.

But in college at Auburn University, he studied music and played the tuba and baritone sax. After graduating, he spent a year as a junior high music teacher before heading to business school at the University of Tennessee where he studied logistics and transportation.

The experience as a music teacher still comes in handy, Clark has said. “I often tell people I learned everything there is to learn about leading people from 250 seventh graders,” Clark said in an interview with Auburn’s alumni association in 2017. “Once you’ve taught 250 seventh graders to play instruments in unison, everything else is pretty straightforward.”

While Clark was going to business school in Tennessee, then scrappy startup online book seller Amazon was exploring the state for the location of one of its first warehouses. The company’s head of operations visited Clark’s class and the MBA student impressed the exec as part of a team presenting on improving warehouse schematics.

Graduating from business school in 1999 at the height of the Internet bubble, the next step was obvious. The day after graduation, he flew to Seattle and started in Amazon’s “Pathways” leadership development program. He’s been with the company ever since.

It’s quite a different path to Amazon than that of Jeff Wilke, 53, the man Clark is replacing.

Wilke grew up in Pittsburg, where he loved to tinker with computers and write software code. He attended Princeton University, majoring in chemical engineering, before getting an MBA from MIT. Though Wilke joined Amazon the same year as Clark, 1999, he had already had a varied career including writing software at Andersen Consulting and as a vice president and general manager of pharmaceutical fine chemicals at AlliedSignal.

Despite the lack of Wilke or Bezos’s Ivy League pedigree, Clark quickly moved up the ranks of Amazon’s logistics operation, from being the operations manager of a fulfillment center in Kentucky in 2001 to general manager of all Northeast warehouses in 2003. By 2010, he was vice president of North American operations and in 2013 was promoted to his current job, senior vice president of worldwide operations.

That same year, Clark gave President Barack Obama a tour of a giant Amazon warehouse in Chattanooga. But he also stopped to give workers a pep talk. “It’s work you do which makes this possible,” he told them.

Clark has been in charge of Amazon’s entire supply chain, delivery, and customer service. Amazon’s stores and its Prime membership program also fall under his purview. He was a big proponent of Amazon’s $775 million acquisition of warehouse robot maker Kiva in 2012 and helped Amazon create its own air delivery network in 2016.

While those areas have experienced tremendous growth under Clark, they have also had challenges.

Reports have criticized unsafe working conditions in Amazon warehouses and some workers in Minneapolis even went on strike on Prime Day last year. But after John Oliver, host of HBO’s Last Week Tonight show, highlighted warehouse problems last year, Clark shot back on Twitter, where he frequently defends the company’s reputation. Oliver was “wrong on Amazon” which offers a “safe, quality work environment in our facilities,” he tweeted.