Q: I recently saw Kenneth Branagh on the Stephen Colbert show. When Shakespeare’s Henry V came up, Colbert referred to it as “Henry Five,” Branagh as “Henry the Fifth.” Are both correct?
A: The customary way to pronounce Henry V is “Henry the Fifth,” though some people think it’s creative or cute to say “Henry Five,” while others who say it that way may perhaps be unfamiliar with the usual pronunciation.
We suspect that Colbert was being cute. A creative example would be Dancing Henry Five, the title of a mixed-media work in which the choreographer-writer-director David Gordon deconstructed and reconstructed Shakespeare’s play.
Shakespeare apparently pronounced it “Henry the Fifth” (or, rather, “Henry the Fift,” as the name was written on the title page of the 1600 quarto of the play). The earliest texts of Shakespeare’s plays were printed in quarto format, with each printed sheet folded into four leaves.
The numbers following the names of monarchs in other Shakespeare plays are similarly spelled out on the title pages, as in these examples from the 1596 quarto of Edward III, the 1597 quarto of Richard III, and the 1598 quarto of Henry IV, Part 1.
When Roman numerals are used to differentiate monarchs, popes, and others with the same name and position, the custom is to pronounce them as ordinal numbers. (Ordinal numbers, like “first,” “third,” and “fifth,” indicate place or order in a sequence, while cardinal numbers, like “one,” “three,” and “five,” indicate how many.)
Customarily, Roman numerals are also spoken as ordinals when used to identify family members with the same name (“Adlai E. Stevenson III”), but spoken as cardinals on clock faces (I, II, III, etc.) and in movie sequels (The Godfather, Part III). Roman numerals can go either way in sports events: Super Bowl XLVI (cardinal, “forty-six”) and XXIV Olympic Games (ordinal, “twenty-fourth”).
Although the Anglo-Saxons had their own Germanic names for numbers, they used lowercase Roman numerals for the figures. So, the Roman numeral v was the figure that represented the Old English word fíf (five) or fífta (fifth). In fact, the two usages were sometimes combined in the same passage.
The entry for the year 900 in The Anglo-Saxon Chronicle, for example, says King Ælfred died “syx nihtum ær ealra haligra mæssan” (“six nights before the All Hallows mass”) after ruling his kingdom “oþrum healfum læs þe .xxx. wintra” (“a year and a half less than thirty winters”).
Roman numerals were generally used for calculations in Old English (roughly 450-1150) and Middle English (1150-1500). Arabic numerals were introduced in Europe during the Middle Ages, but took centuries to replace most uses of Roman numerals in English.
A search of the Early English Books Online database suggests that the use of ordinal numbers to identify English monarchs showed up in the early 1500s, with the numbers sometimes written as Roman numerals and sometimes spelled out.
For example, The Statutes Prohemium Iohannis Rastell, a 1527 compilation of public general acts, by the English writer and printer John Rastell, has numerous references to numbered kings, including “The vi. yere of henry viii” … “kynge Edwarde the thyrde” … “The .ij. yere of. Richard .ii.” (The letter “j” was sometimes used for the final “i.”)
from Grammarphobia https://www.grammarphobia.com/blog/2017/07/henry-v.html