Antoni Gaudí was a Spanish architect known for designing unique structures in Barcelona using natural forms and vivid colors. Some of his most famous works discussed in the document include Park Güell, Casa Batlló, Casa Milà, and the Basílica i Temple Expiatori de la Sagrada Família. The document provides details on the origins, designs, and architectural elements of these buildings, noting Gaudí's influences from nature and use of innovative structural techniques.