On both worlds, he is the husband of Mary Jackson, and on both worlds, he is in the teaching profession; an unnamed university in "Desperation" and an unnamed school in "The Regulators."
As is the case with a select few characters including himself, Collie Entragian, Kirsten "Pie" Carver, Jim Reed, Cary Ripton, and Audrey Wyler, Peter dies in both books.
On the Earth of "Desperation," he is shot multiple times in the lower abdomen at point-blank range by Collie's standard-issue, large caliber handgun. On the Earth of "The Regulators," he is drained of his mental energies by Tak/Seth after partially losing his sanity beforehand at witnessing the aftermath of his wife's murder at the hands of the Regulators. For reasons unknown (or perhaps simply for amusement), after 'feeding' on him Tak sent Peter's nearly mindless body out to impale itself on the preternaturally large and sharp spines of a cactus that Tak/Seth had "created."