http://www.pcgamer.com/radeon-boss-raja-koduri-leaves-amd/

Earlier this fall, AMD's Raja Koduri announced he was taking a sabbatical, with intentions to return in December. Now, as reported by Hexus, he has chosen to extend his leave permanently. The leave began in September, following the launch of Vega and in an apparent desire for some downtime and relaxation with his family. We can only guess at the huge amount of pressure Raja has been under during his latest tenure at AMD, and time away from it all has given him time for reflection, the result of which is his decision to leave AMD.

Here's the full letter obtained by Hexus: