Regnal number in the context of "Theodo of Bavaria"

A regnal name, regnant name, or reign name is the name used by monarchs and popes during their reigns and subsequently, historically. Since ancient times, some monarchs have chosen to use a different name from their original name when they accede to the monarchy.

The regnal name is usually followed by a regnal number, written as a Roman numeral, to differentiate that monarch from others who have used the same name while ruling the same realm. In some cases, the monarch has more than one regnal name, but the regnal number is based on only one of those names, for example Charles X Gustav of Sweden. If a monarch reigns in more than one realm, they may carry different ordinals in each one, as some realms may have had different numbers of rulers of the same regnal name. For example, the same person was both King James VI of Scotland and King James I of England.

The Angevins (/ˈændʒɪvɪnz/; "of/from Anjou") were a royal house of French origin that ruled England and Ireland and in France in the 12th and early 13th centuries; its monarchs were Henry II, Richard I and John. Henry II won control of a vast assemblage of lands in western Europe that would last for 80 years and would retrospectively be referred to as the Angevin Empire. As a political entity this was structurally different from the preceding Norman and subsequent Plantagenet realms. Geoffrey of Anjou became Duke of Normandy in 1144 and died in 1151. In 1152, his heir, Henry, added Aquitaine by virtue of his marriage to Eleanor of Aquitaine. Henry also inherited the claim of his mother, Empress Matilda, the daughter of King Henry I of England and Matilda of Scotland (who was also the remaining descendant of the royal House of Wessex), to the English throne, to which Henry II succeeded in 1154 following the death of Matilda's cousin Stephen.

In 1189, Henry was succeeded by his third son, Richard, whose reputation for martial prowess won him the epithet "Cœur de Lion" or "Lionheart". He was born and raised in England but spent very little time there during his adult life, perhaps as little as six months. Despite this Richard remains an enduring iconic figure both in England and in France, and is one of very few kings of England remembered by his nickname as opposed to regnal number.

Magnus Eriksson (April or May 1316  – 1 December 1374) was King of Sweden from 1319 to 1364, King of Norway as Magnus VII from 1319 to 1355, and ruler of Scania from 1332 to 1360.

Medieval Swedish kings did not use regnal numbers as part of their title. As the king of Sweden, he is sometimes referred to as Magnus II, Magnus III, or Magnus IV. By adversaries he has been called Magnus Smek (lit. 'Magnus the Caresser'). He is the second longest-reigning monarch in Swedish history after the current king Carl XVI Gustaf, who surpassed Magnus in 2018.