Gary Knell, who has headed NPR for less than two years, is departing to become president of the National Geographic Society. In a memo to the staff of NPR posted online this morning, Knell wrote: 

I will be leaving NPR after my term ends in late fall to join the National Geographic Society as its President and CEO. I was approached by the organization recently and offered an opportunity that, after discussions with my family, I could not turn down.

As President and CEO, supporting NPR's success – your success – has been my highest ambition. Working together, we have put NPR on more solid footing to continue to deliver the highest-quality journalism and programming. We have launched innovative new platforms and made meaningful strides in attracting new audiences and new funding. 

That leaves the nation's flagship public radio syndicate without a chief executive for the second time in two years. Knell's predecessor, Vivian Schiller, was forced to resign in the spring of 2011 after a series of damning allegations about NPR's liberal bias, which she had seemingly fueled with injudicious statements and decisions, including the firing of Juan Williams.

Knell was hired in October 2011 from Sesame Street, where he had been the chief executive. David Folkenflik of NPR reported at the time:

Knell, 57, said he hopes to "calm the waters" at NPR after a rocky year in which the institution lost several top executives and faced renewed challenges to its funding.

While Knell could not stem NPR's fiscal troubles, he did oversee an expansion and enhancement of NPR's presence on smartphones, tablets and computers.

Judging from Twitter, the news of his departure took the media world completely by surprise:

No word, yet, on who will replace Knell at the helm of NPR.