The "Gus" crease is a popular crease for a cowboy hat and has been around since the 1800's.
Old west cowboys liked the "Gus" crease on their cowboy hat because they could grab the narrow part of the crown of their cowboy hat and bow to the ladies. Steve McQueen wore the "Gus" crease on his cowboy hat in the movie "Tom Horn".
However the popularity of the "Gus" crease really grew when Robert Duvall wore it on his cowboy hat in the movie "Lonesome Dove". The crown of the cowboy hat has a dramatic slope from back to front and is still worn by many cowboys today.