In Latin, Caius is an archaic spelling of the Latin praenomen Gaius, pronounced /ga:ius/. In early Latin, the letter C was used for both /g/ and /k/; and the names Gaius and Gnaeus were spelt Caius and Cnaius and continued to be so in inscriptions, after the letter G was introduced, and C was confined to the /k/ sound. Notably, the name of Gaius Iulius Caesar is abbreviated CIC.

In English, Caius is a latinized spelling of the last name of John Keys of Gonville and Caius College, Cambridge.

Caius may refer to:

• Pope Caius (died 296), Bishop of Rome and martyr
• Caius (bishop of Milan), bishop of Milan in the early 3rd-century, saint
• Caius (presbyter), early 3rd century Christian writer
• Caius Largennius (died c. 50), Roman legionary

• Caius of Korea (1571–1624), Catholic missionary, one of the Martyrs of Japan
• Caius Brediceanu (1879–1953), Romanian politician and diplomat
• Caius Gabriel Cibber (1630–1700), Danish sculptor
• Caius Iacob (1912–1992), Romanian mathematician and politician
• Caius Lungu (1989–2025), Romanian footballer
• Caius Novac (1821–?), Romanian footballer
• Caius Welcker (1885–1939), Dutch footballer

• Jean Ferdinand Caius (1877–1944), French botanist and naturalist who worked in India
• John Caius the Elder (fl. 1480), English poet
• John Caius (1510–1573), English physician and second founder of Gonville and Caius College, Cambridge
• Thomas Caius (died 1572), English academic and administrator, Fellow and Master of University College, Oxford

• Caius, in the play King Lear, the name that the Earl of Kent takes when in disguise
• Caius, the protagonist in Coriolanus
• Caius Lucius, Roman ambassador and later general in Cymbeline
• Doctor Caius, a French doctor in The Merry Wives of Windsor
• Caius, a casual nomer used in Camus’ play “Caligula” to refer to the tyrannical emperor of the same name.

• Caius, in Sir John in Love, a 1929 English opera by Ralph Vaughan Williams, based on Shakespeare's The Merry Wives of Windsor
• Caius, in the book The Skystone by Jack Whyte
• Caius, in the Twilight series by Stephenie Meyer
• Caius Ballad, the main antagonist in the video game Final Fantasy XIII-2
• Caius Cosades, Grand Spymaster of the Blades in the video game The Elder Scrolls III: Morrowind
• Caius, in the 1960 film Spartacus, played by John Hoyt
• Caius Lao Vistaille, one of the protagonists in the manga (and later anime based on it) The Titan's Bride
• Caius Qualls, the main protagonist of the video game Tales of the Tempest
• Caius, an AI warrior played by Cameron Monaghan in the film Tron: Ares

• Caius Choirbook, an illuminated choirbook
• Caio (disambiguation)
• Cayo (disambiguation)
• Cai (name)

Name list

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