A Medallion is an item that can be used to rename tamed mobs and to tame Big Cats and Kitties. It is crafted with two Leather, a Diamond and three Gold Ingots. An alternative and much cheaper recipe can be used, which involves using two Leather, and a Gold Ingot.
An alternate recipe can also be used. You need one Gold Ingot and two Leather, compared to the other recipe which uses three Gold Ingots and one Diamond.