Last name Rathnam (Rathnam 
, Ратнам 
) , around the world, is a common cognomen. The cognomen Rathnam is habitual in Fiji, where it is quite a rare surname, Kuwait, and Qatar. Measured by absolute frequency, it most frequently occurs in India, Malaysia, and Saudi Arabia. More frequently, Rathnam is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Rathnam | United States, India, Sri Lanka, Malaysia, Saudi Arabia |
| Ратнам | Ukraine, Kyrgyzstan |
| judo. k. k. rathnam Indian actor and choreographer, IN (b. 1930) |
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| ajay rathnam Indian actor, IN (b. 1958) |
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| a. m. rathnam film producer, IN |
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| sukumar rathnam Ph.D. University of Texas at Austin 1993 |
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| padma sukumar rathnam Ph.D. University of Texas at Austin 1995 |
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| christopher rathnam researcher (ORCID 0000-0003-3111-4687) |
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| karthik rathnam Indian actor (b. 1997) |
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