Otto Ferdinandovich Retowski was a Prussian and later Russian malacologist, entomologist and numismatist.

Otto Roquette (April 19, 1824 – March 18, 1896) was a German author.

Otto Karl Julius Rosenberg was a Russian scholar who created a system of organizing Chinese characters in a dictionary format, which eventually resulted in the Four Corner Method.

Otto Karl Seeck was a German classical historian who is perhaps best known for his work on the decline of the ancient world. He was born in Riga.

Johann Ernst Otto Stobbe was a German historian and law professor born in Königsberg.

Otto Stolz was an Austrian mathematician noted for his work on mathematical analysis and infinitesimals. Born in Hall in Tirol, he studied in Innsbruck from 1860 and in Vienna from 1863, receiving his habilitation there in 1867. Two years later he studied in Berlin under Karl Weierstrass, Ernst Kummer and Leopold Kronecker, and in 1871 heard lectures in Göttingen by Alfred Clebsch and Felix Klein, before returning to Innsbruck permanently as a professor of mathematics.

Friedrich Gottlieb Otto Sutermeister was a Swiss folklorist and professor at the University of Berne who collected and revised numerous folk tales, legends, fables, and proverbs.

Ottó Tolnai was a Yugoslav and Hungarian writer, poet, and translator, and a recipient of the Kossuth Prize. He was one of the most versatile and outstanding figures of Hungarian literature in Vojvodina. His works have been published in Serbian, Hungarian, Polish, Slovenian, and German.

Otto, Prince of Bismarck, Count of Bismarck-Schönhausen, Duke of Lauenburg, born Otto Eduard Leopold von Bismarck, was a Prussian and later German statesman and diplomat.

Otto von Botenlauben or Botenlouben, the Count of Henneberg from 1206, was a German minnesinger, Crusader and monastic founder.