At the age of 11, Yaakov Yisrael was recruited for the Novorodock Yeshiva under the great R. Yosef Yosel Hurwitz. The young man progressed rapidly and at the age of 19 was sent by R. Yosef Yosel Hurwitz to head a yeshiva in Rogatshov. At that time Yaakov Yisrael was conscripted into the Russian army where he continued to strictly observe all mitzvot in spite of the harsh conditions. His disciple, R. Ben Zion Bruck, sent him a gemara Succah and a Chaye Adam from which he studied assiduously. He insisted on wearing a summer uniform in the winter since there was no problem of shatnes. One volume of his Kehilas Yaakov contains the Torah he composed while in the army. He was appointed Rosh Yeshiva of the Novorodock yeshiva in Pinsk. In Bialystock he studied under R. Avrohom Jofen. His fame grew and the Chazon Ish heard of his great scholarship, but equally as important, of his yirat shamayim, and sought him as husband for his sister.
The Steipler wrote many works, his magnum opus being the multi-volume Kehilas Yaakov, containing his unique analysis of most of the tractates and concepts of the Talmud. There are several volumes of letters (Karyana DIgarata) and several volumes written by a disciple, Rabbi A. Horowitz, describe his daily life (Orchos Rabbeinu). There is an interesting volume of letters to an American psychologist, Dr. Yaakov Greenwald, in which The Steipler advises him on psychological problems (Eitsot VHadrachot).
Though he held no official position, The Steipler was universally recognized and was consulted by individuals from all walks of life on every imaginable problem and many claimed that he displayed knowledge which was inconceivable by natural means. In his relation with people he seemed both tough and tender, but as one who knew him very intimately said, he would give someone a slap in order to sweeten the judgment. (Lhamtik Hadinim)
Sources: Orthodox Union