Avraham ben Avraham, known as the Ger Tzedek ("righteous convert") of Vilna, is a figure of the tradition of the Jews of Lithuania, Poland and Russia. According to the accounts he was originally Count Valentine (Walenty) Potocki, a son of one of the great Catholic noble families of Poland, born in the late seventeenth or early eighteenth century. Historians have found no trace of him in the archives, but a contemporary testimony from 1755 by Rabbi Yaakov Emden, in Vayakem Edut BeYaakov, speaks of "a great prince from the family of Pototska" who converted in Vilna, was imprisoned for a long time and died sanctifying God's Name.

In the most widespread version, while studying in Paris he and his friend Zaremba frequented the shop of an old Jew whom they always found bent over a volume of Torah; he taught them Hebrew and Scripture. Although Polish law punished conversion from Christianity to Judaism with death, he went to Amsterdam, one of the few places in Europe where a Christian could openly embrace Judaism, and there entered the covenant of Avraham, taking the name Avraham ben Avraham. He then returned to Vilna and hid in a nearby town, Lida or Ilye according to the version, where he lived as a Torah student.

Denounced by a Jew with whom he had quarreled, he was arrested, interrogated and tortured. He immediately admitted his conversion and refused the pardon, wealth and honor promised him if he returned to Christianity; even his mother's pleas could not sway him. According to tradition the Vilna Gaon, then twenty-nine years old, offered to rescue him by means of holy Names, but he refused, preferring to die al kiddush Hashem.

He was burned alive in the square of Vilna on 7 Sivan 5509 (1749), the second day of Shavuot. On the way to the stake he sang the words of the prayer "Aval anachnu amecha bnei britecha, bnei Avraham ohavecha," a melody later sung in the Volozhin yeshiva and by Rabbi Isser Zalman Meltzer every motzaei Yom Kippur. The Church forbade burial of his ashes; one Jew, Leiser Zhiskes, obtained part of them by bribery, and they were buried in the Jewish cemetery.

The Vilna Gaon said that all the years he had lived as a Jew were a tikkun for Avraham Avinu, and before his own death asked to be buried next to him. After the destruction of the old Vilna cemetery, the ashes were reinterred together with the Gaon's remains in the new ohel in the Vilnius cemetery, where a small monument is dedicated to him. The Chafetz Chaim is quoted as saying that had ten Jews been present to say Kaddish when the Ger Tzedek was executed, the Messiah would have come at once.