Amit Fulay served as a Product Manager at Google since 2010, most recently as Head of Product for Real-Time Communications. In other words, he was the head of Allo, Duo, WebRTC, and other projects within the company. Fulay announced on Twitter today that he has left Google, and now works at Facebook.
Today is my first day at Facebook - accepted their friend request :)
Excited about the opportunity to serve so many users.
— Amit Fulay (@amitfulay) January 8, 2018
It's not clear what he is specifically in charge of at Facebook, as his account biography simply says 'Product @ Facebook' (and his LinkedIn hasn't been updated yet). It's possible he is in charge of Facebook's own messaging efforts, but that is purely speculation.
It's not clear at this time who is replacing Fulay at Google, and only time will tell if Duo or Allo will change direction under new leadership. Duo has enjoyed moderate success, especially since it is included with many new Android devices, but Allo is still struggling to increase its user base.