A
Tiefling is a
mythic or
fictional creature in
TSR's
Planescape setting for
AD&D. Tieflings are said to be the
offspring or (more usually) descendents of
demons, although this is seldom if
ever stated explicitly. Their goodly counterparts are
aasimar.
Cambions and
alu-fiends/
alu-demons are sometimes considered to be kinds of tiefling, as are
fey'ri.
This was one of my very first nodes. I used '
demon' to indicate '
fiend' for the good of non-
RPG-playing
noders. Tief is the
German for deep, and the designers state that this is the main reason for the name, although the similarity to '
Teufelchen', an
imp, is useful.
Addendum: Tieflings and aasimar make perfectly good PC races in
Third Edition, provided that it is remembered that their base abilities are as good as those of most other races with one character level. See Chapter Two of the
Dungeon Master's Guide for full details.
Further Addendum: The newest edition of the
Forgotten Realms Campaign Setting has a system in it for creating
Tieflings,
Aasimar and
Genasi as
Player Characters.