Definition of "IRCer"

Changes your nickname — the name by which other IRCers see and refer to you — to anything you'd like (but remember that nine characters is the maximum nick length).

1995, Donald Rose, Internet Chat quick tour

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