The Lady is a
goddess on the
Discworld, though she might fall closer to an
Anthropomorphic Personification, like
Death or
Fate. She is described as a
stunningly beautiful woman with emerald-green eyes. She is rather
capricious (the only serious worshippers she had were some gamblers who tried to built a temple to her, but died shortly thereafter), and often helps mortals when they least expect it.
She is, of course, Lady Luck, but it's wise not to address her by name.
When the gods in Dunmanifestin play their games, The Lady often plays against Fate, and usually wins. She claims that she plays not to lose, rather than to win, and she never sacrifices a pawn if she can help it. One of her favorite pawns is Rincewind the inept "Wizzard".