Othmar Reiser or Otmar Rajzer (21 December 1861 – 31 March 1936, Pickern) was an Austro-Slovenian ornithologist and naturalist who worked as curator of the bird collections in the natural history museum at Sarajevo, working there from its foundation for thirty-three years during which he explored various regions including the Balkans and South America and collected specimens. Several species have been named after him.