The uncle of Esther who looked after her and urged her to do everything in her power to effect the deliverance of the Jews throughout the Persian empire. See Chapter 16.
Mordecai or Mordechai (מָרְדֳּכַי, Standard Hebrew Mordoḫay, Tiberian Hebrew MordÅḵay - the son of Jair, of the tribe of Benjamin, is one of the main personalities in the Book of Esther in the Hebrew Bible.