You (or The Viewer) are a character of Blue's Clues, Blue's Room, and Blue's Clues & You!, situated and addressed to as a part of the fourth wall. On occasion the viewers are classified as the voice of several children (usually listed as "Steve's Friends" in the credits), even when you don't actually interact with the onscreen characters vocally. Steve and Joe, among other characters, talk to You throughout most episodes through the screen (or the fourth wall.)
You and the other viewers are the most important character of Blue's Clues.
While the viewer/viewers can be/look like anyone or anybody, some episodes have shown several visual interpretations of the viewer.
You have appeared in every episode, although not credited as an official character.
Although not having officially been credited, You are a true character as per taking part within the show itself.