Dave Spector (alternatively known to some as Dali) is a man found in the White Desert. One stands in front of a tunnel. Killing him then entering the tunnel will grant the player access to one of two areas: Monoe's tunnel or one where white fires burn, arms and legs protrude from the ground, and severed heads spin in the sky.
Another Dave Spector can be found several screens north of the tunnel, northwest of the entrance to the Block World. 
He and Seccom Masada-sensei are the only two characters that walk backwards in the game, as evidenced here at 0:51.