Carl Otto Reventlow (actually Karl [Carl] Christian Otto; born 1817 in Store Heddinge (Denmark), died in 1873) became notable as the developer of a mnemonic system. The type of relationship (if any) he had with the Reventlow family of old Holstein-Mecklenburg nobility is not known.
Otto took up studies in philology at the University of Copenhagen but soon focused on the art of memory enhancement. After publishing a textbook on his mnemonic system in 1843[1], he travelled widely in Germany to popularize it. His most notable lectures were given in Leipzig, but also in Prague. A dictionary that substituted mnemonic terms for numbers[2] and a guideline for the use of mnemotechnics in schools[3] which listed some 3,000 mnemotechnically annotated facts from history and geography courses followed in 1844 and 1846, respectively.
The novelty of Otto's "substitution method" was disputed almost immediately[4][5], his opponents stating it to be just one more derivative of the method proposed by Aimé Paris. However, it received highly favorable reviews as well[6].
Otto subsequently involved himself in the revolutionary events of 1848, and came under police investigation in 1849[7]. Apparently he was the Carl Otto-Reventlow who took over a Cincinnati radical, anti-monarchist periodical for German-speaking exiles, the Hochwächter, in 1857[8]. He appears to have had some contact with Karl Marx, who referred to him in extremely derogatory terms in at least one of his letters[9].