Rabbi Yehuda Zev Segal was the head of a yeshiva, to whom the Rebbe wrote in the mid-1950s. He may be Rabbi Yehuda Zev Segal, the renowned Rosh Yeshiva of Manchester, but the published letters do not identify him further, and the identification has not been confirmed. The summary below is drawn from the letters themselves.
The Rebbe's letters encourage his work in the yeshiva: standing firm in one's sacred task and sharing the light of Torah (IK 2141); equipping students to stand strong in the material world they will enter (IK 2413); success in the yeshiva through effort together with blessing (IK 3322); and yeshiva study rooted in love and awe of G-d (IK 4266). Another letter discusses yiras Shamayim in daily deeds and the enduring light of Pesach (IK 2570).
See also: Education – Running a school; Education – Yeshiva students.