King Boo/"Boo Boy"

Who?
King Boo is a fictional Mario character.

For a full review, follow this Yellow Brick link

What does he have anything to do with Marker Comics?
In Night at the Nintendo Museum, Captain Tonnybrow has to face King Boo (or Boo Boy, as he calls King Boo), who parodies Atilla the Hun in Night at the Museum.

Where did that weird nickname come from?
In some episode of "Winnie the Pooh", Tigger refers to Pooh as 'Pooh Boy'.