User blog:Dean.kumi/Oda strongly hints the design of admiral Green Bull in volume 70 of One Piece!

On the last page of One Piece Volume 70 Oda drew a picture of a very famous japanese actor who is called Toshirou Mifune with horns on his head. He played for example the legendary Samurai Musashi Miyamoto. Considering that all the Admirals´appearance and, to a certain extent, their personality is based on famous actors in their most popular role, this drawing is somewhat interesting. It is also peculiar that Oda drew Mifune with horns and now introduced a character named Ryokugyuu (Green Bull).

Source: http://i.imgur.com/xKcSAhJ.jpg