In Resident Evil 4 Wii Edition for the Wii, there are a few characters you can unlock for use in Mercenaries Mode.
To unlock them, you have to get four star rankings or higher on specific maps:
Ada Wong – Get a four star ranking or higher on the Pueblo map
Albert Wesker – Get a four star ranking or higher on the Waterworld map
HUNK – Get a four star ranking or higher on the Island map
Jack Krauser – Get a four star ranking or higher on the Castle map