Which character is the best choice for me to write about the theme of identity?

Misha would be the best choice for your paper. Misha is called by many names and perceived as many things over the course of the novel. He is called a thief, a gypsy, and a Jew. He claims to be a gypsy because of Uri's advice.... because the Jews are being killed. Misha goes to America and becomes Jack.... he becomes a husband and father.... then he is divorced and becomes nothing. In the end, his daughter finds him, and he gets to be a father again. He even gets to be a grandfather.