One afternoon, Apollo was walking through the palace at Mount Olympus when he came across Eros, Aphrodite's son as well as the young God of Love, who happened to be in the form of a child and "playing" with his bow and arrows.
Apollo found the sight of Eros' childish form and miniature bow so humorous that he burst into laughter, and mocked him, going as far as to show off his own golden longbow and brag about his archery prowess. An indignant Eros then secretly determined to teach the God of the Sun a lesson. The next afternoon, when Apollo was walking by the riverside in Thessaly, Eros shot a golden arrow of love straight into Apollo's heart, and then shot a lead arrow of indifference into the heart of Daphne, a beautiful naiad who happened to be bathing nearby.
This caused Apollo to fall instantly and hopelessly in love with Daphne, and he decided that he had to marry her. Most unfortunately for him, due to Eros' arrow of indifference and the numerous tales of how the loves of the gods almost always met with tragic ends, Daphne had sworn off love affairs with gods a long time ago, and therefore spurned his advances. A chase erupted, with some banter on Apollo's side, and though Daphne initially was the faster one, she started to tire.
When she reached a dead end, she cried to Gaea for help, and the goddess took pity on her and transformed her into a laurel tree just as Apollo threw his arms around her. Heartbroken by the transformation that meant he had irrevocably lost her, Apollo burst into sobs of despair, and declared that though he had failed to win her love, he still would honor her in his own unique way: he would wear a crown of her leaves, and the laurel tree would become a symbol of victory for all time.
Daphne was consistently mentioned throughout the book. Apollo referred to her as one of his two greatest loves, and still secretly mourned her loss, to the extent where any reminders - intentional or not - of her would almost reduce him to tears. While he initially blamed Eros for his loss of her, Apollo later confessed in an honest song that he had no one to blame but himself, for he should have let her go when she rejected his courtship.
In Percy Jackson's Greek Gods, Daphne was described to be beautiful in the typical way that naiads were. However, due to Eros' arrow of love, when Apollo first saw her, he thought she was even more beautiful than Aphrodite.
In The Hidden Oracle, Apollo described Daphne to be a beautiful woman with fair skin, offset green eyes, a slightly crooked nose, a lithe form, and lips that he had never stopped dreaming of. She also had a lilac scent, and there was a resemblance between her and Meg McCaffrey.