He was the father-in-law of Rabbi Chaim Michael Dov Weissmandl, and played a minor role in the Bratislava Working Group's efforts to save Slovak Jews from the Holocaust.
After his bar mitzvah, Shmuel Dovid left home to study at the yeshiva in Prešov, headed by his uncle, Rabbi Noach Baruch Fisher.
Weissmandl tried to dissuade Ungar from accepting the offer, arguing that it would be a mistake to leave an established community like Trnava for Nitra, which was only about 200 years old and had 3,000 Jews.
Weissmandl married his Rav's daughter, Bracha Rachel, in 1937,[6] and became Ungar's right-hand man in all aspects of running the yeshiva.
Besides his position as the chief rabbi of Nitra, Ungar was appointed vice president of the Moetzes Gedolei HaTorah, the supreme religious body of World Agudath Israel, in 1935.
[7] Persecution of Jews began even before World War II in Slovakia, where the Munich Agreement of 1938 carved Czechoslovakia into separate states.
Slovakia became a totalitarian state run by the Catholic priest Jozef Tiso, who allied with Nazi Germany and supported discrimination against his country's Jews.
[4] Defying a Nazi order to remain at home on that first day of deportations, Ungar walked to the synagogue to spend the third meal of Shabbat with his flock.
To assist students who were still being accosted and sent to forced labor camps, the yeshiva constructed hiding places under the bimah and above bookcases in its study hall, in the event of Nazi raids.
They made their way to Bistritz, which was under partisan control, but when the Germans attacked that city the following month, they fled and spent the winter hiding in mountain caves and subsisting on starvation rations.
While terror and fear were others' constant companions, he was concerned with how to fulfill the mitzvah of hearing the shofar blasts on Rosh Hashanah.
These were published under the title Ne'os Desheh ("Lush meadows", a line from Psalm 23; the second word in Hebrew, דשא, contains his initials, שמואל דוד אונגר).