Inimitable describes someone or something that is impossible to copy or imitate.

// Courtnay delivered the speech in her own inimitable style.

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“In a nation whose professed ideals include freedom, liberty and independence, every American is charged with an individual self-examination. ... Such a searching self-examination helps us discover our precepts, ethics, ideals, principles, and purpose—a sense of mission. Reverend King discovered his mission as a teenager at Morehouse College. Although the son, grandson and great grandson of ministers, Reverend King initially aspired to be a lawyer. Then he encountered the inimitable Dr. Benjamin Elijah Mays, President of Morehouse College. ... The rest is history.” — David C. Mills, The (Nashville) Tennessee Tribune, 13 Apr. 2023

Something that is inimitable is, literally, not able to be imitated. In actual usage the word describes things so uniquely extraordinary as to not be copied or equaled, which is why you often hear it used to praise outstanding talents or performances (or uniquely talented and incomparable individuals). (The less common antonym imitable describes things that are common or ordinary and could easily be replicated.) Inimitable comes, via Middle English, from the Latin adjective inimitabilis. Be careful not to confuse it with inimical or inimicable, two adjectives meaning “hostile” or “harmful”; those words come from a different Latin root.