According to the biblical book of Esther (Esther 1:14, 1:16-21), Memucan was one of the seven vice-regents of the Persian King Ahasuerus. It is not stated in the text explicitly, but it is the generally accepted belief that Memucan and Haman were the same person.
When Queen Vashti, Ahasuerus' consort, refused his order to display herself at the king's banquet, Memucan advised the king to depose her and replace her with a more worthy wife. Memucan further advised the king to issue a decree throughout his domain declaring his action, so that all women would learn a lesson and honor and respect their husbands. The decree was translated and transcribed into each language and script of the empire, so that each man would be "master in his own house." 
1: The Oxford Study Bible: Revised English Bible with the Apocrypha. Edited by M.J. Suggs, K.D. Sakenfeld, J.R. Mueller (New York: Oxford University Press 1992) pps. 501-502.