Osmund Saddler (voiced by Michael Gough) serves as the main antagonist of Resident Evil 4.
Saddler is the leader of a religious cult known as Los Illuminados, which seeks to control the world. He has converted the villagers into his cult, and now controls them due to the Plaga parasites in their bodies. His plan for Ashley Graham was to put the parasite into her, and send her back to the US to infect the President, allowing Saddler to begin his conquest of the world.
Saddler encounters Leon S. Kennedy and Ashley frequently, first setting his minions on them, then using his growing power over their Plaga-infected bodies to control their actions.
He briefly fought Ada Wong, after she helped Leon free Ashley for the final time. Though he was defeated, he still managed to capture her.
Finally, Leon confronted Saddler on a platform high above the island, and after freeing Ada, watched as Saddler transformed himself into a massive, multi-legged monstrosity. Despite Saddler's considerable strength in this form, Leon managed to defeat him.