Mordecai, the son of Jair, son of Shimei, son of Kish, a Benjaminite
He was carried away from Jerusalem among the captives carried away with Jeconiah king of Judah, whom Nebuchadnezzar king of Babylon has carried away. He adopted orphaned Esther as his daughter, but she was the daughter of his uncle (so, his cousin?). (Esther 2:5-7)
When Esther was brought into the harem, he advised her to keep her Jewish heritage private. He walked in front of the court of the harem every day to learn how she was and what was happening to her. Surely it was good news, since she was favored by Hegai and was advanced to the best place in the harem. When the virgins were gathered together the second time, Mordecai was sitting at the king's gate. Bigthan and Teresh, two eunuchs who guarded the threshold, became angry and sought to lay hands on King Ahasuerus. Mordecai told Esther who told the king in his name, which led to their hanging and a recording of the event in the book of the chronicles. (Esther 2:8-23)