Rabbi Yitzchok Blazer, is also known as Rav Itzele Peterburger (after the city of St. Petersburg where he was Chief Rabbi). Rabbi Blazer was a great leader of European Jewry prior to World War I and the author of a scholarly work Pri Yitzchok. At the young age of only twenty five, he became the Chief Rabbi of St. Petersburg, a position he held for 16 years.

He was one of the leading and most famous disciples of Rabbi Yisrael Salanter, the founder of the Mussar ethics movement, and after Rabbi Salanter's death became the successor of the Mussar movement. In 1876 Rabbi Yisrael Salanter established a Kollel in Kovno. Its purpose was the furtherance of Rabbinics and Ethics by supporting and guiding exceptional Torah scholars in their development as authorities. The project received the blessings and support of the world renowned Rabbinical authority and Chief Rabbi of Kovno Rabbi Yitzchok Elchonon Spector. It was joined by such luminaries as Rabbi Naftoli Hertz (later Chief Rabbi of Jaffa), Rabbi Naftoli Amsterdam, Rabbi Chaim (Telzer) Rabinowitz, and Rabbi Yosef Yozel Horwitz (the "Alter of Novardok"), among many others. The Kollel was eventually named Kollel Knesses Bais Yitzchok in memory of Rabbi Spector.The true glory of the Kollel was realized under the leadership of Rabbi Yitzchok Blazer whose rousing lectures were the Kollel's life-force.

Rav Itzele became the Chief Rabbi of Petersburg, the capital of Russia at the time. Although reluctant to assume any leadership role, he was goaded into the position by his great mentor Rabbi Yisroel Salanter. One time, the city hosted a convention of the leading Rabbis of the generation. During the convention the great Rabbi of Brisk, Rabbi Yosef Dov Soloveitchik, posed a very difficult question which was raised by his son Rabbi Chaim Soloveitchik . A great Torah debate broke out among the rabbis, who were all trying to answer the question, each one showing the depth and breadth of their abilities. At the end, Rabbi Yosef Dov Soloveitchik gave two original answers, one his own and one from his son Rabbi Chaim. During the entire debate Rav Itzele, the Chief Rabbi, just sat there quietly not uttering a word. This made Rabbi Yosef Dov Soloveitchik wonder what kind of scholar Rav Itzele really was and how did earn such a good reputation. Later when Rabbi Soloveitchik happened to peruse the sefer authored by Rav Itzele, Pri Yitzchok, he was astonished that the question posed, and the two answers presented by Rabbi Soloveitchik were in fact not original but had already been written and published by Rav Itzele! Nevertheless he made no mention of it at the debate and allowed everyone present to think that he had nothing to offer the discussion! Such was the greatness and humility of greatness of Rav Itzele Peterburger.

Rabbi Blazer emigrated to Jerusalem in 1904 and spent the last few years of his life in Jerusalem. At first he accepted the leadership of the Kolel Lita & Zamut, but soon He was enjoined by the Chief Rabbi of Jerusalem Rabbi Shmuel Salant to help with matters concerning the community in general, and in particular to join the Board of Governors of the Rabbi Meir Baal Haneis Salant charity fund, to help oversee the collection and distribution of the funds. In the Rabbi Meir Baal Haneis Salant archives there are hundreds of letters from donors all over the world written to Rabbi Shmuel Salant and Rabbi Yitzchak Blazar in matters relating to the Rabbi Meir Baal Haneis Salant charity fund.

Rabbi Yitzchok Blazer also established a "House of Ethics" or Bais Hamusar on Straus Street where he lived. He passed away in 1907, two years before Rabbi Shmuel Salant. Rabbi Chaim Berlin related that Rabbi Yitzchok Blazer had left a special request in his will that there should be no eulogies for him after his death. Rabbi Chaim Berlin asked the Chief Rabbi of Jerusalem Rabbi Shmuel Salant if they were required to abide by the humble last wishes of Rabbi Blazer, since it would definately be a meritorious deed to eulogize a person of his greatness and stature. Rabbi Shmuel Salant ruled that they had no choice but to oblige to to heed his final wishes. A few days after his passing, Rabbi Chaim Berlin related that Rav Itzele came to him in a dream thanking him for honoring his request. Rabbi Chaim Berlin then asked Rav Itzele what issues of Jewish law the Heavenly Court sitting in Judgment is stringent about. Rav Itzele told him that a human being cannot fathom the depth and detail of the Judgment. They were particularly exacting on the purity of a persons speech. This coming from a person who had mastered the art of silence!