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?