Piter is a Mentat Assassin to House Harkonnen. He helps plan Duke Leto's demise, and he breaks Yueh's Imperial Conditioning by torturing his wife, Wanna. After the defeat of House Atreides, Piter is given stewardship over Arrakis but is killed in Duke Leto's poisonous gas attack, making his reign one of the shortest in literary history.
In a way, Piter plays the foil to Hawat. Both men have blind spots in their Mentat abilities (clicky-click on over to Hawat's character analysis for more on what a Mentat is). But Piter's blind spot stands in opposition to Hawat's. Whereas Hawat's pride in his abilities and his extreme sense of loyalty cause him to fail, it's Piter's love of violence and worldly pleasures that lessens his abilities as a Mentat. Piter's desire to serve himself causes the lapses in judgment leading to the escape of Paul and Jessica, as well as to Piter's own death.
And that is a shame. Piter's back-and-forth banter with Baron Harkonnen is pretty entertaining.