Lucasfilm has confirmed the identity of the First Order stormtrooper dubbed "TR-8R" by internet meme artists after he yelled "traitor!" at Finn in The Force Awakens.
The stormtrooper's true designation is FN-2199, and he was one of Finn's squadmates prior to the hero blasting his way out of Starkiller Base and joining the Resistance. Dubbed "Nines" by his friends, he trained alongside Finn (then known as FN-2187) before joining a riot control squad that uses betaplast shields and lightsaber resistant Z9 batons for subduing crowds at odds with the First Order's regime.
Nines appeared in the Greg Rucka book Before the Awakening, which includes a nifty illustration by Phil Noto showing the red-haired stormtrooper sat in the background. On the big screen, he was voiced by David Accord, a sound editor from Skywalker Sound, while stunt actor Liang Yang gave him his moves.
It has been hinted that we may not have seen the last of Nines...