Baron Harkonnen

Millennia before the Baron, Valya Harkonnen leads the Sisterhood that will become the Bene Gesserit. She comes from a disgraced and banished House Harkonnen and blames the Atreides for her family's downfall. The rivalry the Baron takes to the extreme is already there.

Emperor Shaddam IV takes Arrakis from the Harkonnens and gives the planet to Duke Leto. It's a trap: the Baron and the Emperor have agreed to destroy the Atreides there, far from Caladan.

On Giedi Prime, the Baron plans the attack with his Mentat Piter de Vries and his nephew Glossu Rabban. He has a traitor inside the Duke's household, Dr. Yueh, whose wife is a Harkonnen prisoner.

With Arrakeen's shields shut down by Yueh, the Harkonnens and disguised Sardaukar take the city. Leto is brought before the Baron, but Yueh had put a poison gas capsule in the Duke's tooth. Leto bites down, the gas kills Piter de Vries and others in the room, and the Baron floats away, wounded.

The Baron orders Paul and Jessica dumped in the desert to die, with no marks of an execution, and hands Arrakis to Rabban with orders to squeeze out every last gram of spice.

The Baron watches Rabban fail against the Fremen raids and spice output collapse. He changes his bet: he puts his younger nephew, Feyd-Rautha, in charge of Arrakis, fresh from celebrating his birthday by killing Atreides prisoners in the arena on Giedi Prime.

Feyd answers with brute force and destroys Sietch Tabr, not knowing it pushes Paul south.

The Emperor lands on Arrakis with the Sardaukar, and the Baron comes along. The Fremen strike with Atreides atomics and sandworms in the middle of a storm and take the imperial court. In the same assault, Gurney Halleck kills Rabban.

Paul finds the Baron, calls him grandfather and stabs him to death.

In Frank Herbert's novel, the Baron is far more talkative and scheming, and Piter de Vries plays a bigger part in the plots. Paul learns he is the Baron's grandson already in the desert tent, still in Book One. And the Baron doesn't die at Paul's hands: he's killed by Alia, Paul's sister, still a small child, with the poisoned gom jabbar. In the prequel novels by Brian Herbert and Kevin J. Anderson, his obesity is explained as a disease Reverend Mother Mohiam gave him on purpose.