A Spark of Yaakov
The Hebrew word nassi (leader) is made of the first letters of the phrase nitzotzo shel Yaakov Avinu, "a spark of Yaakov our father." The Megaleh Amukos teaches that the soul of every leader of Yisroel is an offshoot of the soul of Yaakov, the father of the Jewish people.
Source: Megaleh Amukos, section 84