Who Was the First Jew?

Inspired by a question in the comments on this video...

Some people will say that Abraham was the first Jew, but that seems silly to me. Abraham was a Hebrew, but wasn't a Jew by any definition I've ever heard.

It really depends on what you mean by the word. It is derived from Judah (Yehudah in Hebrew), so in one sense, Judah would be the first Jew. After Israel was split into two kingdoms, citizens and residents of the southern kingdom could be called Jews (or Yehudim). During the Babylonian captivity, most people known to have descended from Israel became commonly known as Jews, no matter what tribe or kingdom their ancestors came from, and that usage continued through the Greek and Roman Empires.

In the New Testament, the term Jew could refer to anyone who was ethnically an Israelite, anyone who lived in the Roman province of Judea, anyone who had converted to one of the sects of Judaism, or to the Jewish religious leadership centered in Jerusalem, depending on the context.

Today, the term Jew usually refers to people in one of two categories:

1. People who are known or believed to be descended from one of the tribes of ancient Israel, no matter what tribe and no matter what religion they practice. Some bigoted people will claim that you can practice any religion and still be a Jew, unless that religion accepts Jesus (aka Yeshua) as the Messiah.
2. Anyone who practices one of the varieties of Judaism, no matter who they are descended from.

By definition #1, the first Jew could be Reuben. I think that's too anachronistic since the term comes from the name of Reuben's younger brother, Judah, so I would go with Judah instead.

By definition #2, the first identifiable Jew might be Nehemiah or Ezra, but I don't think we can point to a specific person. The religion evolved over time, and I'm certain that the religion of Nehemiah wouldn't have looked much like the religion of the Pharisees in Yeshua's day.