Nikolai Adamovich Okolo-Kulak (1867-1927) – a mechanical engineer, inventor, state councilor, head of the main Riga workshops of the Riga-Oryol railway, founder and director of the Russian Technical School in Riga. >>

Boris Oks (1928-2012) – Habilitated Doctor of Engineering, professor of the Riga Technical University. >>

Vladimir Okun (1943) – a soloist of the Latvian Opera, director.

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Alexander Olbik (1939-2018) – a journalist and writer. >>

Sergey Oleynikov (1919–2004) – a sworn advocate. >>

Afanasy Ordin-Nasсhokin (1605–1680) – a Russian diplomat and politician in the reign of Alexey Mikhailovich.  Russian vaivode of Koknese (Kokenhusen). >>

Leonid Orekhov (1930–2007) –  Doctor of Engineriing (Dr. sc. ing.), Docent of the Riga Technical University. >>

Mikhail Orlov (1918-1944) – the Great Patriotic War (World War II) Participant, Hero of the Soviet Union. Born in Latgale (East Latvia). >>

Oleg Orlov (1947)  – a vocalist, tenor, soloist of the Latvian National Opera, soloist of the Tallinn National Opera, soloist of the Krakow Philharmonic, vocal teacher at the Latvian National Opera. >>

Nina Orlova (1894-1980) –  a teacher of Russian language. >>