Garegin or Karekin Pastermadjian, better known by his nom de guerre Armen Garo or Armen Karo was an Armenian activist and politician. Armen Karo was a leading member of the Armenian Revolutionary Federation for more than two decades. He was one of the masterminds of the 1896 occupation of the Ottoman Bank in response to the Hamidian massacres, and of Operation Nemesis, in which several perpetrators of the Armenian genocide were assassinated. Between 1918 and 1920 he served as the first ambassador to the United States from the First Republic of Armenia.

The occupation of the Ottoman Bank by members of the Armenian Revolutionary Federation took place in Constantinople, the capital of the Ottoman Empire on 26 August 1896. In an effort to raise further awareness and action by the major European powers, 28 armed men and women led primarily by Papken Siuni and Armen Garo took over the bank which largely employed European personnel from Great Britain and France. Stirred largely due to the inaction of the European powers in regard to Hamidian massacres started by Sultan Abdul Hamid II, the Armenian Revolutionary Federation members saw its seizure as a means to bring full attention to their plight. At the time, the Ottoman Bank served as an important financial center for both the Empire and the countries of Europe.