The following characters make an appearance in Resident Evil 4 HD:
Previously a rookie cop caught up in Raccoon City on the first day on the job, Leon was approached by the United States government soon after the event. He became a government agent, honing his skills and attitude. He was about to be given assignment to protect the President and his family when Ashley, the president's daughter, was kidnapped. Now he's been dispatched to Spain to search for her...
Daughter of the president of the United States, Ashley was kidnapped and taken to Spain to fulfill a plan for a powerplay. Even though she's twenty, she tends to be rather helpless and comes off as a bit younger
Like Leon, Ada was initially introduced in Resident Evil 2, as somewhat of an enigma. That remains here, as she brushes in and out of scenes, leaving Leon to wonder what exactly she's up to. She carries on with her nonchalant attitude but there's obviously something more to her to be seen.
Krauser is a bit mysterious, showcasing obvious superhuman abilities and having a past relationship of some kind with Leon. He faked his own death to get out of the government and is now seemingly working on two different sides. He obviously has an issue with Ada despite them supposedly being on the same mission. More than anything, he wants power.
Ramon Salazar, despite being rather short and looking quite old, is actually only twenty years old. He's infected with Las Plagas but has a different type than the foot soldiers as he has some control of over it, albeit not the same amount as Saddler. He helps Saddler out mostly to supposedly make up for the actions of his ancestors. Salazar tries to remove Leon as a threat several times while also communicating with him over the codec.
Saddler is the main villain in the game. Ultimately, he simply doesn't like the idea of the United States policing the world and wants to put a stop to that by gaining power himself. In order to do so, he decides to use Ashley Graham, the president's daughter, to try to take control of the government in some form.