Ger Tzedek/Tzadik earliest sources and definition

Question

As I understand a "Ger Tzedek/Tzadik" is a fully converted follower of the Torah of Moshe. According to Hilchot Melachim 10:3-4, a "Ger Tzedek" is defined as someone who has confirmed their conversion (out of a sincere and deep conviction in the truth of the Jewish religion, without any other motivation whatever). Later on (in verse 12), we see that a "Ger Tzedek" must non-selectively accept all of the mitzvot of the Torah of Moshe. The convert who accepts the responsibility to fulfill the mitzvos – the Torah’s path of tzedek – is therefore called a ger tzedek. It is this commitment which enables the convert to become a member of Israel – the people of the Covenant. Just as all Israel became the people of the Covenant by proclaiming at Mount Sinai: 'Everything that Hashem has spoken, we will do and we will hear' (Exodus 24:7), so too, the convert joins the people by making a similar commitment (like Ruth). Our tradition finds a reference to this idea in the following Divine statement: 'The convert who dwells with you shall be like a native among you' (Leviticus 19:34). According to the tradition, these words are revealing the following guideline which the rabbinical court that accepts the convert must follow: 'Just as the native Israelite accepted all the words of the Torah, so does the convert. (Toras Kohanim)'

But what i would like to know is how this term 'Ger Tzedek' came to exist: what are it's earliest sources? and can it be literally found in the Tenach?

Answer 1

Here's an interesting article on this subject.

In short, the term ger tzedek is only used in a small fraction of the gemara when speaking about converts. In most cases, even when "full converts" are spoken of, the simple title ger is used. The term ger tzedek was introduced in order to emphasize the differences between a full convert, and a ger toshav who is only obligated to the Seven Laws of Noah.

Examples where this differentiation is required (more in the article):

• Gittin 57b:

  תנא: נעמן גר תושב היה, נבוזראדן גר צדק היה

• Yevamot 48b:

  כשהוא אומר "וגרך אשר בשעריך" - הרי גר צדק אמור, הא מה אני מקיים "והגר"? - זה גר תושב

The reason for the specific choice of tzedek is also discussed there, mainly since the word tzedek appears many times in the bible referencing the Torah, the Shechina, etc.

Answer 2

It could be from Tannaitic literature Midrash or the Septuagint, the Greek translation of the Hebrew Bible. We know for sure that the rabbis (Second Temple times) understood גר תושב (ger toshav) to mean a non-Jew who fulfills some biblical commandments while (ger she-nitgayyer) or (ger tzedek), meaning “a righteous ger," refers to a convert who underwent the practice of conversion. 

Answer 3

The earliest source I can find is in the Shemona Esrei we say daily

על הצדיקים ועל החסידים ועל זקני עמך בית ישראל ועל פליטת סופריהם ועל גרי-הצדק.

Interesting to note in the Selichos of the fourth day of the Aseres Yemei Teshuva from Rabbeinu Gershom Meor Hagola

גר צדק הראשון לכל נציבים, בן שלש הכירך יושב כרובים.

Thanks to Daat.ac.il for this answer