The transformer is a neural network architecture introduced by Google in 2017 that revolutionized natural language processing. Unlike previous sequential models, transformers process all parts of an input simultaneously using a mechanism called ‘self-attention,’ allowing them to understand long-range relationships in text. Virtually all modern large language models — including GPT, Claude, Gemini, and Llama — are built on the transformer architecture. Its efficiency and scalability enabled the current generation of powerful, general-purpose AI systems.