Chaim Shimon Zev Rubin corresponded with the Rebbe in the 1950s, raising questions of Torah and Chassidus. No reliable published biography is available; the summary below is drawn from the letters themselves.
The Rebbe's letters to him discuss redemption through the study of the Zohar, and practices of Torah study (IK 2444); daily Tanya study and Torah as life (IK 2702); the editing of a phrase in Shaar HaYichud VehaEmunah (IK 3121); allusions in the name Yosef Yitzchak and their spiritual significance (IK 3291); the significance of the numbers 19 and 36 in Torah thought (IK 4091); Israel's exile and redemption and the power of the lion (IK 4533); and the unique role of Pesach Sheni (IK 6899).
See also: Torah study – The Rebbe's answers on verses, Rashi, Gemara and Midrash; Accuracy – Torah texts and editions.