A hereditary peer is a member of the British peerage whose title and associated privileges are inherited according to the specific terms of a royal letters patent or an ancient writ of summons. These titles are categorized into five ranks—Duke, Marquess, Earl, Viscount, and Baron—and historically represented the 'Peers of the Realm,' functioning as a legislative and judicial class within the House of Lords. While their role was fundamentally transformed by the House of Lords Act 1999, which significantly reduced their automatic right to sit in Parliament, they remain the primary custodians of the realm's high titular honours.
Technically, a hereditary peerage is an incorporeal hereditament, a form of property that descends through a bloodline, usually limited to heirs male of the body. In the context of heraldry, these individuals are entitled to specific external ornaments on their achievements, including coronets of rank, supporters, and the peer’s helmet. Historically, the peerage served as the vital link between the Crown and the landed gentry, anchoring the feudal hierarchy through land tenure and military or advisory obligations to the Sovereign.