The phrase "ugly duckling" is a well-known idiom that refers to someone or something that appears unattractive, unfashionable, or unwanted at first glance but later reveals hidden qualities or beauty. The term originated from the fairy tale written by Hans Christian Andersen in 1843, where an ugly duckling transforms into a beautiful swan after maturing. In modern usage, the phrase is often used to describe someone who initially feels out of place but eventually finds their own unique identity and sense of self-worth.