He was the main force behind Yahoo's push into native advertising.
When Gentzel joined Yahoo last fall, several of his colleagues generally spoke well of him to Business Insider, saying he was "very good with clients" and "very well-connected."
One source however, suggested Gentzel was not Yahoo's first choice. Another wondered if he might have been "out of his depth" at Yahoo, citing that Forbes - Gentzel's previous employer - was a $100 million annual business, while Yahoo's revenues charted closer to $5 billion.
Several other sources generally praised Gentzel, calling him well-polished, ambitious and super-smart.
Gentzel had been seen as an important addition to CEO Marissa Mayer's executive circle.
At the time, Yahoo's client relationships were in need of some smoothing over, after Mayer and Yahoo's then-head of Americas Ned Brody attempted to share head of sales duties between themselves. That effort was apparently unsuccessful.
Digiday says that in the past few months, ad buyers were still unhappy with Yahoo's products, some of which never managed to "gain big enough audiences to impress advertisers."