Judaism is a religion practiced by humans on at least three universes: Earth One, Earth Thirty-Eight and Earth-X. A person practicing Judaism, regardless of their ethnicity, is considered Jewish.
Earth One Edit
Judaism was practiced since the ancient times, back during the era of Devarim mystics, responsible for the creation of powerful artifacts. It has survived throughout many centuries, along with the rise of Christianity, and is still practiced on Earth in the 21st century. The worshipers celebrate the holiday of Hanukkah around the same holiday period as Christmas, lighting the holy symbol of menorah. Another holy symbol is the Star of David, also similar to the Seal of Solomon, an ancient Jewish king. Jewish practitioners, such as Felicity Smoak, do not recognize the holiday of Christmas. A priest is known in Judaism as a rabbi. Martin Stein was forced to become a rabbi by his father before he could enroll at MIT, allowing him to minister the wedding of Caitlin Snow and Ronnie Raymond.
In the Earth-X universe, after the Nazi regime of New Reich took over Earth, practitioners of Judaism were persecuted, forced to wear the Star of David to signify their status, and were routinely thrown to concentration camps as if they were criminals. Among such prisoners was Felicity Smoak's Earth-X doppelgänger, whom the Sturmbannführer asked Oliver Queen to execute, trying to see whether he was truly Führer Oliver or an imposter.