Ottilie Davida Assing (11 February, 1819 – 21 August, 1884) was a 19th century German feminist, freethinker, and abolitionist. Born in Hamburg, she was the eldest daughter of a prominent Jewish physician, David Assur, who converted to Christianity upon marriage and changed his name to Assing. Her mother was the poet Rosa Maria Varnhagen Assing, who was friendly with other literary women, including Clara Mundt and Fanny Lewald, and prominent in liberal circles that supported (but failed to achieve) social revolution in 1848.
After the great fire of Hamburg in 1850, Assing and her sister Ludmilla went to live with their uncle, the prominent literary figure and revolutionary activist, Karl August Varnhagen von Ense. His wife, the noted Jewish writer and saloniste Rahel Varnhagen, was long dead. Ottilie and Ludmilla soon came to blows in that household, and Ottilie left, never to return. In 1852, she emigrated to America, settling in New York and eventually in Hoboken, New Jersey. She supported her self by writing articles for the Morgenblatt für gebildete Leser and often wrote under a male pseudonym.
Assing read the Narrative of the Life of Frederick Douglass, and was impressed. In 1856, she went to Rochester to interview Douglass. They struck up an immediate friendship and, possibly, an affair. For the next 26 years, they attended meetings and conventions together. At first, she wrote general interest pieces about culture, but soon her writing focused on the abolitionist movement. While Assing was in Europe, trying to establish her claim to her sister's estate (including her mother's, and the Varnhagens' papers) she read in a newspaper that Douglass was to marry his 20-years-younger white secretary, Helen Pitts. She had already been diagnosed with incurable breast cancer. Assing committed suicide in a public park in 1884. As per the will left in her hotel, her correspondence with Douglass was burned and Douglass received her meager estate (the bulk of the family fortune having been given away on a whim by her sister.)