Cognomen Gaio (Gai 
, Gaio 
, Гай 
) , throughout the world, is a common family name. The cognomen Gaio is habitual in Monaco, where it is quite a common surname, Gambia, and Portugal. Not in comparison with a country's population, the name is most common in China, Italy, and India. Very seldom, Gaio is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Gai | Brazil, Italy, Sudan, China, India |
| Gaio | Brazil, Italy, China, India, Portugal |
| Гай | Kazakhstan, Armenia, Belarus, Russia, Ukraine |
| גאיוס | Israel |
| gaio ofonio tigellino Roman praetorian prefect (AD c.10-69), IT (b. 10) |
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| gaio musonio rufo 1st century AD Roman Stoic philosopher, IT (b. 25) |
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| gaio valerio flacco 1st-century Roman poet and writer, IT (b. 45) |
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| gaio calpurnio pisone Roman senator and conspirator against Nero (died 65 AD), IT (b. 50) |
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| gaio giulio giovenale politician, IT (b. 50) |
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| gaio fufio gemino 1st century AD Roman senator and ally of the empress Livia, the mother of Tiberius, IT (b. 50) |
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| gaio cecina largo Roman politician, consul 42, IT (b. 50) |
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| gaio anicio ceriale 1st century AD Roman senator and consul, IT (b. 50) |
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gaio ottavio father of emperor Augustus. Roman general, praetor in 61 BC, praefectus propraetor in Macedonia in 60-59 BC, IT (b. 100) |
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| gaio elvidio prisco Roman philosopher and statesman, IT (b. 50) |
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| gaio avidio nigrino late 1st/early 2nd century Roman senator and consul, IT (b. 50) |
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| gaio calpurnio pisone crasso frugi liciniano late 1st /early 2nd century Roman senator, consul and conspirator, IT (b. 50) |
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| gaio elvidio prisco suffect consul 87 AD, IT (b. 55) |
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| gaio cornelio miniciano IT (b. 50) |
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| gaio cassio parmense 1st century BC Roman politician and writer, IT (b. 74) |
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