A Kage (meaning "Shadow") is the leader of one of the five most powerful ninja in their respective villages. They are collectively known as the Five Kages. If a Kage has held their position for several decades, as was the case with the Third Hokage, younger ninja are likely to have become stronger than they are. In such cases, the Kage may retire and give the title, once granted, is held permanently. This creates a case where there are two Kage at the same time, with only one of them active, as it was with the Third and Fourth Hokage. After the Fourth died, the Third came out of retirement ( the same happened to the Third Tsuchikage and the Fourth Tsuchikage).
The Kage stand equally with the rulers of their countries, oversee the activites of their villages, and are the leaders of ninja socirty. They typically are the ones who send the ninja teams out on their missions and make the decisions regrading the safety of the village. The five Kage are:
Since the creation of jinchuriki, it has become tradition for the host to be selected from the family of their village's own Kage. In this way, the jinchuriki not has strong ties of loyality to their village and leader (mainly like their parents, grandparents, and great ancestors of a jinchuriki), but they also serve to show off the Kage's might.