Amazon Prime head departs company after 18 years

The Amazon (AMZN) executive behind Amazon Prime is leaving the online retailer after 18 years.

Greg Greeley, vice president of Amazon Prime and delivery experience, announced his exit on LinkedIn Monday night, saying in a post that the time had come for him to "take on a different challenge." He did not specify what that challenge would be.

Greeley also voiced gratitude to the "tens of thousands of Amazon team workers" that he'd worked with during his time at Amazon, and voiced admiration for CEO Jeff Bezo's "heartfelt" letter to shareholders in 1997. 

"That letter described a unique approach for a public company, and the vision it contained was even more powerful than I fully understood at the time," Greeley wrote.

News of Greeley's departure comes weeks after he took on added responsibilities related to Whole Foods, the upscale grocery chain acquired by Amazon last year. 

Amazon last month rolled out free two-hour delivery of Whole Foods groceries through the retailer's Prime Now service in areas including Cincinnati and Dallas. One analyst called the move the "beginning of the 'unlocking' of the real value of the While Foods acquisition."

Meanwhile, Amazon competitors Target (TGT) and Walmart (WMT) have been beefing up their grocery business. Target put in a new management team for its grocery department last year, while Walmart's Jet has introduced a higher-end grocery line aimed at millennials.