The correct plural of Yeoman Warder.
All warders must be former SNCOs with at least 22 years of service. They must also hold the LS&GCmedal. NCOs from the Army, Royal Marines and Royal Air Force are eligible to apply, but members of the Royal Navy are not, because while members of the other services take oaths to the Crown, members of the Navy take an oath to the Admiralty.
This principle was first introduced by the Duke of Wellington who, when appointed as Constable of the Tower of London, was reportedly horrified by the slack discipline of the Yeomen Warders (who could buy and sell their positions) and decreed that all warders should henceforth be drawn from sergeants of the Army in good standing.
Although officially responsible for guarding the Tower, they are now basically the world's best-dressed tour guides. And the loudest.
All are required to memorise the history of the Tower (or at least the Yeomen Warders' version) and they give regular free guided tours. Don't stand in the front row without earplugs.