Oskar Osipovich Gruzenberg (in German transliteration - Grusenberg; Russian: Оскар Осипович Грузенберг; also known as Israel Gruzenberg Hebrew: ישראל גרוזנברג; 1866–1940) was a prominent defense attorney.
His father died from anthrax when he was a child, plunging the family into poverty.
He made a name for himself defending striking workers and members of the revolutionary parties.
He also participated in the defense of Beilis in the infamous case of blood libel.
His body was buried in Trumpeldor Cemetery in Tel Aviv.