I'm looking to gather some more background, context, sources and opinions, regarding Mordechai's religiousness, or lack thereof.
This was the topic of a recent comment thread on Was Darius Jewish?, specifically on @avi's answer.
Though this was not the topic of the question nor the answer, a side comment turned into a long thread on this.
Instead of hashing it out there, and just between us, I thought it would be a good idea to gather some additional voices.
So, to the issue:
Many well-known midrashim pose Mordechai as a tzaddik, a religious leader, and even a member of the Sanhedrin. I'm sure we all learned these at one point or another.
On the other hand, reading the Megilla as a "story", focusing on the pshat, but taking into account the historical and cultural context, in addition to relevant background added by other books in the Tanach (such as Melachim Bet, Divrei Hayamim, and other Nevi'im) - it would seem that this was not the case. At the least, there is no evidence or basis for the "religious figure" theory, but rather the evidence seems (at least to me) to point in the opposite direction.
Now, taking into account the intended ambiguity, which is one of the most fundamental motifs of the Megilla, and the obvious historical distance, I don't expect to find "the one true history"...
But I am interested in hearing, what is the basis for the "religious leader" theory? Is there evidence for this, or is it "just" Midrash* ? What was the original source? What is the Midrash based on? (Obviously besides the Midrash itself, and the persuant discussions in e.g. Gmara*... )
Or, alternatively (and preferably), sources and explanations for the opposite theory?
EDIT: To emphasize, I am referring to Mordechai's "back story". Even according to the "non-religious" theory, there is plenty of room to allow for a change of heart as a result of the Purim events. Therefore anything that relates to his situation after the fact (such as @follick's excellent source in Nechemia) would be besides the point.
EDIT2: I don't intend on ignoring the midrashim, nor do I expect to be completely independant of them. Rather, I'm interested in the basis of those midrashim, as these are usually based on something, be it a reference, alliteration, extraneous wording, "secret" story, etc.
(*) I'm not belittling the importance of those Midrashim or the discussions in the Gmara, of course, but it is both important and extremely difficult to discern which stories are intended to be accepted literally, as "historical fact", and which not.
Hence this question.