The red-haired Shanks is one of the most important characters in Eiichiro Odas One piece. Introduced at the very beginning of the story, Shanks played a pretty important role in paving the way for Luffy to make his way to becoming the Pirate King. By entrusting Luffy with his Straw Hat, Shanks asked the young pirate to return it to him one day when he becomes a Grand Pirate. Obviously, Shanks was always a pretty pivotal figure in the wider story, but most things about him still remain unknown.
https://gamerant.com/one-piece-shanks-past-explained/ One Piece: Shanks’ Past Explained