W4-R was a designation of a heavy Skytrooper Battle droid. It was used by followers of the disgraced Battalion Commander Tassar, who were constructing a new Star Fortress on Rakata Prime's surface. Following the death of Empress Vaylin in 3630 BBY they were discovered by the Eternal Alliance forces and a strike team was dispatched to stop Tassar and her efforts, destroying W4-R.
Behind the scenes
W4-R appears in the game files for Star Wars: The Old Republic under npc.exp.uprisings.rakata_prime.landing.boss_2 category. However, it does not appear in the live version of the "Landing Party" Uprising.