Baggy-pants Leon is a soldier of the Survey Corps appearing in the gag preview of Volume 17 in Volume 16 of the Attack on Titan manga.
Baggy-pants Leon is a middle-aged man with light hair cut short and combed back, and pronounced sideburns running down to his jaw. He wears the standard uniform of the Survey Corps, though his pants inexplicably hang low at his waist, exposing his boxers.
Baggy-pants Leon appears to be a sloppy, ill-mannered man, openly wearing his pants far lower than acceptable for a soldier of the Survey Corps and arriving late to moments of critical importance. Despite his shortcomings, Leon seems to possess a bravado and determination to face his enemies head-on.
Appearance: Baggy-pants Leon is a middle-aged man with light hair cut short and combed back, and pronounced sideburns running down to his jaw. He wears the standard uniform of the Survey Corps, though his pants inexplicably hang low at his waist, exposing his boxers.
Personality: Baggy-pants Leon appears to be a sloppy, ill-mannered man, openly wearing his pants far lower than acceptable for a soldier of the Survey Corps and arriving late to moments of critical importance. Despite his shortcomings, Leon seems to possess a bravado and determination to face his enemies head-on.
Baggy-pants Leon in the story: When a massive Abnormal Titan threatens to destroy Squad Levi, Baggy-pants Leon meets up with his comrades to assist in the encounter. Connie is shocked to see Leon, who apologizes for his late arrival.
Abilities: Baggy-pants Leon likely has little to no potential as a combatant against the Titans, given how loosely his vertical maneuvering equipment sits on his waist.
Source: Attack on Titan Wiki, available under CC BY-SA 3.0.