Rabbi Menachem Zev ("Volf") Greenglass was born in Łódź, Poland, in 1917 to a family of Aleksander chassidim. At about twenty he joined the Lubavitch yeshivah in Otwock, where he was later appointed a mentor to a select group of students. During World War II he escaped with fellow students on transit visas issued by the Japanese consul Chiune Sugihara, traveling through Russia to Japan and Shanghai; he was among nine Chabad students who then received visas to Canada.
In Montreal he was one of the founders of the Chabad institutions and of the yeshivah, Tomchei Temimim (the Rabbinical College of Canada), where he served for many decades as mashpia, a spiritual mentor to thousands. He had a close relationship with the Rebbe from the 1940s, when the Rebbe headed Merkos L'Inyonei Chinuch and Kehot, and worked with him on publishing Chabad works; he himself co-authored works on Chabad customs, including Sefer HaMinhagim. He passed away on 22 Teves 5771 (December 29, 2010), at 94.
The Igros Kodesh contains an extensive correspondence with Rabbi Greenglass, spanning decades. Among its themes:
Publishing Chassidus. Many letters concern the work of Kehot and spreading Chassidus: updates on publishing and book distribution (IK 096, 117, 208, 236), printing maamarim as a gift under specific conditions (IK 182), and sending newly printed kuntreisim (IK 419, 7825). The Rebbe urged active participation in spreading Chassidus despite any rationalizations against it (IK 117), and put communal benefit before personal convenience in Torah projects (IK 236).
Torah questions. The Rebbe answered his questions in Chassidus, halachah and custom — the order of the three kelipos in Tanya (IK 045), Divine names (IK 096), customs such as the tallis katan and distributing the Haggadah (IK 185), and chassidic stories and details of tefillin (IK 7826).
Communal responsibility. The letters also show the Rebbe relying on him in communal matters in Canada: urgent care for the Jewish community of Winnipeg after the river flood, with special attention to children's education (IK 619), and swift, collaborative action on visas for others in need (IK 7825, 419). A 5703 (1943) letter, published on Chabad.org, urged him not to postpone establishing Beis Rivkah, a school for girls, stressing that Torah education for girls is "a matter of life itself."
Sources: Wikipedia; Lubavitch.com ("Renowned Teacher, Holocaust Survivor, 94"); Chabad.org; Mishpacha ("The Mashpia of Montreal"); and the Rebbe's letters cited above.