The brightest Jew of all time was Moses. The second brightest Jew of all time was Rabbi Judah HaNasi. The third brightest Jew of all time was Rashi. Moses gave the world the Torah. Rabbi Judah gave the world the Oral Torah. And Rashi gave the world the key to understanding both with his unrivaled commentaries into their meaning. Without these three Jews, there would be no Judaism today.
"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." - Manuel II Palelologus
Well, I am a Christian, so the brightest Jew of all time would be Jesus Christ, the Word made flesh.