The Brotherhood of the Horse (aka Knights of Azeroth or Knights of Stormwind) was the official name of the kingdom of Stormwind's knights before the First War. Most of the knights were killed fighting in the last battles of the war, but took many orcs with them. They were the most feared warriors in the Azerothian army. Many of the knights who fell to the orcs were transformed into death knights by Gul'dan.
The Brotherhood once occupied the tower of Karazhan, which would one day become the home of the sorcerer Medivh. Because of this, the tower and its surrounding buildings sometimes show their influence, such as horse heads in various ornamentation.
The most notable, and only known, member of the Brotherhood was Anduin Lothar, who became a knight and rose to the position of 20th Armsman. After the First War, in recognition of his services to his people, Sir Lothar was given the title of Regent Lord of Azeroth.