Definition of "MUDer"

IRCers frequently use nicknames and MUDers can not only choose a name, but also a gender and a character.

1996, Rye Senjen, Jane Guthrey, The Internet for Women, page 94

Why would a man take on a female identity? How does one determine the sex of a MUDer?

2002, Elizabeth L. Paul, Taking Sides: Clashing views on controversial issues in sex and gender