Casimir Dunin Markievicz (Polish: Kazimierz Dunin-Markiewicz [kaˈʑimʲɛʂ ˈdunin markˈjɛvit͡ʂ], 15 March 1874 – 2 December 1932), known as Count Markievicz, was a Polish portrait, category and landscape artist, playwright and theatre director, and husband of the Irish revolutionary Constance Markievicz.
The Dunin Markievicz family held land in Malopolska Province (today Ukraine), and had an estate in a town of Zywotow (today a village of , Polish: Żywotówka) where Casimir grew up. Markievicz attended the State Gymnasium in Kherson, and studied law at the University of Kyiv. In 1895 he transferred to the École des Beaux-Arts in Paris. While in Paris, he met and married Jadwiga Splawa-Neyman. They had two sons, Stanislas and Ryszard, but the marriage did not last. Jadwiga returned to Ukraine where she and Ryszard died in 1899. He met Constance Gore-Booth in 1899, and the two mixed in the bohemian Paris society of the time. In Paris, Markievicz was known as "Count Markievicz". When Constance's family enquired as to the validity of the title, they were informed through Pyotr Rachkovsky of the Russian Secret Police that he had taken the title "without right", and that there had never been a "Count Markievicz" in Poland. (An online list of counts of the imperial Russian nobility does not include anybody by the name of Markiewicz.) However, the Department of Genealogy in Saint Petersburg said that he was entitled to claim to be a member of the nobility. Markievicz and Gore-Booth married in London in 1900, and their daughter, Maeve, was born the following year. From 1902 the couple lived in Dublin. He continued to be known as "Count Markievicz" (and Constance as "Countess Markievicz"), and in the 1911 census gave his occupation as "Count (Russian nobility)". Stanislas later said in a letter that his father had not been a count.