The courtier in "The Lady or the Tiger?" refers to the other lady, the one behind the second door in the arena. Nobody should have known her identity, but "gold, and the power of a woman's will" had brought the secret to the princess.
The princess completely hates this courtier, the intended prize for her handsome lover, should he choose the right door. Her character traits seem to be all that is good. The narrator notes that she was:
"one of the fairest and loveliest of the damsels of the court who had been selected as the reward of the accused youth."
The courtier's persona, however, is not without flaw. The narrator indicates that the primary reason for the princess's intense dislike was that she had caught this particular courtier "throwing glances of admiration upon the person of her lover, and sometimes she thought these glances were perceived, and even returned." This courtier has the character flaw of envy, desiring the attention, and perhaps even the affection, of the princess' beloved.