NK-3 represented the identification for a pair of IG-100 MagnaGuards who functioned as the dedicated protectors of the N-K Necrosis droid while it was located on Kashyyyk.
The assassin droid known as IG-72 seized two MagnaGuards for the scientist Treun Lorn. These MagnaGuards were intended to contribute to Nycolai Kinesworthy's studies involving the remnants of General Grievous. The outcome of this research was N-K Necrosis, a lethal creation modeled after Grievous. The NK-3 units were employed to educate the Necrosis droid in the lightsaber styles previously taught to Grievous's own guard detail.
Ultimately, the NK-3 units, along with Necrosis, were overcome by a diverse group of spacers within the Myyydril Caverns situated on Kashyyyk. The droids' wrecked bodies were then looted for anything of worth.
The NK-3 units were featured in the video game Star Wars Galaxies, a massively multiplayer online role-playing game created by Sony Online Entertainment and released by LucasArts, before the game's shutdown on December 15, 2011.