"a fellow named Simon who entitled himself Bar-Kochba"

This is Simon ben Kosiba (d. 135 AD), who led the 3rd Jewish Revolt of 132-135 AD, and was given the title Bar-Kokhba ("Son of the Star") in reference to the prophecy of Numbers 24, 17 ("...there shall step forth a star out of Jacob, and a sceptre shall rise out of Israel, and shall smite through the corners of Moab...". The revolt had been prompted by a series of laws enacted by Hadrian, forbidding the Jewish practice of male circumcision and expelling Jews from Jerusalem (now renamed Aelia Capitolina). Bar-Kokhba established a Jewish state, which he ruled as "Nasi" (Prince) for three years, before his stronghold at Betar was overcome by the legions. According to Cassius Dio, 580,000 Jews were massacred following this defeat. All Jews thereafter were permanently excluded from Jerusalem, and the province of Judea merged with other territories to form "Syria Palestina." After the failure of the revolt, Rabbinical sources referred to ben Kosiba as Simon Bar-Kozeba ("Son of Lies").