Many would argue Manhattan is the world's most famous island. This 59 km² island at the heart of New York City hosts iconic landmarks: Empire State Building, Times Square, Central Park, Broadway, Wall Street, and the Statue of Liberty (on nearby Liberty Island). It is a global symbol of finance, culture, media, and urban energy.
Other contenders (e.g., Bali, Ibiza, Hawaii's Big Island, Great Britain) are famous for different reasons—tourism, nature, history—but Manhattan's concentration of globally recognized sites and its role as a metonym for "New York City" give it unparalleled name recognition.