All chassidus traces its roots to the Baal Shem Tov. Izhbitza-Radzyn is one of many branches of the Pshyscha school, founded by the Yid Hakodesh (“Holy Jew”) and grown by the Rebbe Reb Bunim, Rabbi Simcha Bunim. The 1st Rebbe in the Izhbitza-Radzyn line was Rabbi Mordechai Yosef Leiner, a chassid of the Rebbe Reb Bunim. After the passing of his Rebbe, Rabbi Leiner followed his childhood friend and learning partner, Rabbi Menachem Mendel Morgenstern, where the latter became known as the Kotzker Rebbe. They formed a partnership there until the year 5600 (fall 1839), when Rabbi Leiner set out on his own to be a Rebbe, first going to his hometown, Tomaszow, before eventually settling in Izhbitza.
Rabbi Mordechai Yosef is better known as The Izhbitzer, and the author of Mei Hashiloach (“Waters of Siloam”). His innovative, and sometimes controversial philosophy, has been a popular study by scholars. Two of his most famous talmidim were Rav Tzadok HaKohen of Lublin and Reb Leibele Eiger, grandson of the famous Talmudist Rabbi Akiva Eiger. Rav Tzadok wrote many seforim, and much of the Izhbitzer’s hashkofa is explained in these works.
Rabbi Leiner’s son, Rabbi Yaakov Leiner (author of the “Beis Yaakov on the Torah” and “Sefer Hazmanim” on Passover and Shavuos), continued the dynasty. His seforim often build on the teachings of his father, the Izhbitzer. Rabbi Yaakov later moved (1867) from Izhbitza to Radzyn. From this point on, the dynasty became known as Radzyn.
His son and successor, Rabbi Gershon Chanoch Henoch, was renowned for his genius. His Sefer Sedrei Taharos is a unique achievement, beloved by scholars. He compiled Talmud-like folios for the order of the Mishna Code that lacked a Gemara counterpart. It has a Rashi-like commentary and a Tosafos-like commentary, and the pages are laid out the same as Talmud pages.
But he is better known for his research and discovery of the source of the lost blue dye, techeiles, used in tzitzis (“ritual fringes”). After studying all the Torah sources on the subject, he wrote a booklet outlining the criteria for identifying the chilazon, the aquatic species from which the blue dye is formed. After then studying at the world famous aquarium in Naples, Italy, he identified the common cuttlefish, Sepia Officinalis as the chilazon. He made his identification public and then set out to determine a process for making the blue dye. A year later Radzyn was dyeing techeiles, and it continues today. He passed away on 4 Teves in his early 50’s, to be succeeded by his son, Rabbi Mordechai Yosef Elazar Leiner.
Rabbi Mordechai Yosef Elazar Leiner, author of Tiferes Yosef, was Rebbe for nearly 40 years. One of the founders of Agudas Yisroel in Poland, his leadership was marked by great collaboration with the leading Rebbes of Poland. He gave Talmud shiurim according to the mystical teachings of chassidus, in the manner of his great-grandfather The Izhbitzer. He passed away on 26 Shvat 1929.
Rabbi Shmuel Shlomo Leiner eventually took over for his father, the Tiferes Yosef, but it took time and a lot of people to convince him. He was very zealous. He held high standards for Radzyner shuls and would close down any that didn’t meet these standards, e.g. one in which the Gabbai didn’t send his daughters to the local Beis Yaakov school but sent to the public school instead. In spite of efforts to bring him to the USA, he elected to stay with his chassidim. He encouraged his chassidim to fight the Nazis, allowing Jews to escape to the woods. Eventually the Nazis found out who had been causing so much trouble for them and hunted him down. He was executed on the 29th if Iyar in 1942. He went down with a fight, spitting at his Nazi captors.
Rabbi Avrohom Yissochor Englard was appointed to be the head of the Radzyner yeshivos before WWII. He was with the Rebbe Shmuel Shlomo just before he was taken by the Nazis. He spent the rest of the war fighting in the woods with the partisans. During the holiday of Sukkkos, he dug a pit and covered it to create a legally valid Sukkah. After the war he moved to New York. While preferring not to become Rebbe, he eventually relented and moved to Bnei Brak to become Rebbe. He helped to rebuild Radzyn, and his warm manner and outreach efforts brought many people back whose connection to Radzyn and Torah had weakened as a result of the war. He passed away in 2005.
After Rav Englard’s passing, his son, Rabbi Shlomo Englard, Shlita took over as Rebbe in Bnei Brak. He puts out a beautiful weekly kuntres on the parsha, Tiferes Radzyn. Eventually, Rabbi Avrohom Yissochor Englard’s oldest grandson Rabbi Nosson Nochum Englard took over as Rav of the Radzyner shul in Jerusalem. Rav Nosson Englard is now known to many as the Radzyner Rebbe of Yerushalayim. He is famous for his outreach work and can often be seen at Modern Orthodox yeshivos teaching Radzyner chassidus, and his Shabbos tisch is a cross-section of the Jewish community.
A brief lineage of Radzyn may be found here. A list of seforim (many with links to scanned copies) is here.