Rabbi Dr. Hillel haKohen (Philip) Klein (1849 – 1926), born in Baracska, Hungary, was a prominent Orthodox rabbi in Prussia, the Russian Empire, and the United States. He began studying at the Pressburg Yeshiva when he was twelve after which, when he was 16, he attended Azriel Hildesheimer's Yeshiva in Halberstadt. He was appointed dean of a department in the Yeshiva shortly afterwards and spent two years there. He then went to Vienna, and in 1868 he entered the gymnasium there whereafter he studied at the University of Vienna. With the encouragement of Hildesheimer (who by then became Chief Rabbi of Berlin), he moved to Berlin, Germany and enrolled in the Hildesheimer Rabbinical Seminary and the University of Berlin. He received his rabbinical ordination in 1871 and a Ph.D. from the University of Berlin in 1873. He spent some time as an instructor at the University of Berlin, and then accepted a position as tutor for the son of Israel Brodsky in Kyiv, Russia. His rabbinical diploma was conferred by Rabbi Benjamin Hirsch Auerbach of Halberstadt. From 1874 to 1880, he lived in Kyiv. He then served as Rabbi of Libau, Courland from 1880 to 1890. In 1890, he immigrated to America and lived in New York City. There, he was appointed rabbi of Congregation Ohab Zedek, an important Hungarian congregation in the Lower East Side. He was a founder of the war relief movement in the United States when World War Ⅰ began in 1914. He was a leader of Agudath Israel and president of Agudath Israel of America, although he remained partially connected to Mizrachi Zionism. He was also honorary president of the Union of Orthodox Rabbis of the United States and Canada and president of Kollel Shomrei HaChomos.