IT-0 was an NPC, a sadistic interrogator droid onboard the Peace Moon.
A New Generation Edit
On the Peace Moon, Vader confronted Princess, who was being held prisoner there. Vader told her that they were on the trail of those Peace Moon plans, that they'd already managed to trace those plans as far as to a "desert Rebel hideout" who's defensive arsenal impressed even Vader. But the lubrication oil was contaminated with dust, causing the hideout's weapons to jam, so Vader's troops overran the place. Vader had a sadistic droid, IT-0, interrogate Princess.
Later, IT-0 was destroyed along with everything and everyone else onboard the Peace Moon when Luke blew it up.