Cognomen Cayo (Cayo 
, カヨ 
, Гай 
) , worldwide, is a common surname. The cognomen Cayo is habitual in Bolivia, where it is quite a common surname, Japan, and Peru. Much less frequently, Cayo is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Cayo | Argentina, Spain, Bolivia, Peru, Brazil |
| カヨ | Japan |
| Гай | Ukraine, Kazakhstan, Armenia, Russia, Belarus |
| גאיוס | Israel |
| cayo ancio restión (b. 50) |
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| cayo dilio vócula soldier (0100-0070), ES (b. 100) |
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| cayo umidio durmio cuadrato 1st century Roman senator, consul and proconsul, ES (b. 100) |
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| cayo memio brother-in-law to Pompey, ES (b. 105) |
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| cayo aufidio marcelo politician (b. 150) |
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| cayo curcio rufino (b. 200) |
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| cayo julio pisibano (b. 200) |
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cayo quiñones de león y santalla Spanish diplomat (1818-1899), ES (b. 1818) |
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| cayo vea-murguía escalante Spanish politician, ES (b. 1827) |
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| cayo escudero marichalar Spanish politician, ES (b. 1829) |
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| cayo balbuena lópez (b. 1826) |
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| cayo miltos Paraguayan politician, PY (b. 1843) |
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cayo alsina Argentinian aviator and military personnel, AR (b. 1914) |
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cayo sila godoy Paraguayan musician (1919-2014), PY (b. 1919) |
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| cayo vela marqueta Spanish composer (1885-1937), ES (b. 1884) |
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