King of arms is the senior rank of an officer of arms. In many heraldic traditions, only a king of arms has the authority to grant armorial bearings and sometimes certify genealogies and noble titles. In other traditions, the power has been delegated to other officers of similar rank.
A herald, or a herald of arms, is an officer of arms, ranking between pursuivant and king of arms. The title is commonly applied more broadly to all officers of arms.
Heralds were originally messengers sent by monarchs or noblemen to convey messages or proclamations—in this sense being the predecessors of modern diplomats.
Garter Principal King of Arms (also Garter King of Arms or simply Garter) is the senior king of arms and officer of arms of the College of Arms, the heraldic authority with jurisdiction over England, Wales and Northern Ireland. The position has existed since 1415.
Garter is responsible to the Earl Marshal for the running of the college. He is the principal adviser to the sovereign of the United Kingdom with respect to ceremonial and heraldry, with specific responsibility for England, Wales and Northern Ireland, and, with the exception of Canada, for Commonwealth realms of which Charles III is the sovereign. He also serves as the king of arms of the Order of the Garter and his seal and signature appear on all grants of arms made by the college.