Rabbi Shlomo (1738-1792), Chassidic Rebbe in the town of Karlin, Russia (near Pinsk), was killed in the pogroms which accompanied the Polish uprising against Russia.
During the Three Weeks, from 17th of Tamuz to the 9th of Av, we commemorate the conquest of Jerusalem, the destruction of the Holy Temple and the dispersion of the Jewish people.
Weddings and other joyful events are not held during this period; like mourners, we do not cut our hair, and various pleasurable activities are limited or proscribed. (The particular mourning customs vary from community to community, so consult a competent halachic authority for details.)
Citing the verse (Isaiah 1:27) "Zion shall be redeemed with mishpat [Torah] and its returnees with tzedakah," the Rebbe urged that we increase in Torah study (particularly the study of the laws of the Holy Temple) and charity during this period.
Links:
The Three Weeks
You have to begin with the knowledge
that there is nothing perfect in this world.
Our job is not to hunt down perfection and live within it.
It is to take whatever broken pieces we have found
and sew them together to create beauty.