Born in 1766 in what is now the Czech Republic, Aaron Chorin studied as a teenager in the Prague yeshiva under Ezekiel Landau, the foremost European rabbinic scholar of the day, Chorin went on to become one of the very first to propose a program of reforming halakhah. David B. Green writes:
In 1798, Chorin published his first rabbinic pamphlet, . . . in which he controversially argued—as had his teacher Rabbi Landau—that the sturgeon has scales and is therefore kosher. This was a provocative claim, and it elicited unpleasant reactions from other rabbis, particularly Moravia’s chief rabbi, Mordecai Banet, who had already ruled that the fish was treyf. . . .
In 1803, Chorin published a book . . . in which he argued that learned rabbis can adapt Jewish law to current conditions. He also began delineating the customs and commandments that he believed could be dispensed with, which over time came to include not only kapparot, the pre-Yom Kippur custom of [slaughtering] a chicken as a sign of penance, but also more substantive laws like the restrictions on travel and writing on the Sabbath. [He also advocated] shortening shivah, the seven-day period of mourning following the death of a close relative. . . .
Aron Chorin was a fighter, and he seems to have taken satisfaction in provoking his colleagues with his unorthodox rulings. Thus it was . . . that he became the first rabbi to give his endorsement to the changes introduced by the German Reform movement, many of them related to the synagogue service, such as the saying of certain prayers in the vernacular, and the use of an organ on the Sabbath.
Read more on Haaretz: http://www.haaretz.com/jewish/this-day-in-jewish-history/1.734864