This summary is drawn from the Rebbe's letters to him (from the late 1940s to about 5720, 1960), which show him to be a Torah scholar and researcher of chassidic history; I did not find a published biography.
Scholarly questions. The Rebbe discussed with him when the study of secular sciences aligns with Torah values according to Tanya (IK 495), nuanced distinctions in halachic sources regarding Asherah and idolatry (IK 1952), subtle points of Talmudic terminology (IK 6870), and clarified that pikuach nefesh refers strictly to matters of life and death, not mere distress (IK 5839).
Documenting Chassidus. The Rebbe valued precise documentation of chassidic teachings and encouraged efforts to collect them (IK 6817).
After the Previous Rebbe's passing. In a letter from 5710 (1950), the Rebbe reflected on the loss and urged Anash to carry on their mission with added light and responsibility (IK 563).
Sources: the Rebbe's letters cited above.