Who is Piter de Vries from Dune and what is their importance?

Piter de Vries is Baron Vladimir Harkonnen's "twisted Mentat". He is described as a diminutive figure with a musical tenor voice and narrow slits for eyes, tinted blue-in-blue because of his addiction to the spice melange. The Baron is regularly irritated by his talkativeness, and he would love to eliminate him, but he needs his computational abilities. De Vries is accidently killed when the captured Duke Leto bites down on an artificial tooth filled with poison gas, intending to take the Baron with him into death. The Baron escapes, but de Vries falls dead.