Scientists who study the brain try to understand how it performs everyday behaviors like language, memory, and emotion. Scientists learn a lot by studying how these behaviors change when the brain is damaged. Over the past 200 years, they have made many discoveries by studying individuals with brain damage. For example, one patient could not form sentences after damaging a specific area of his brain. The scientist who studied him concluded that the damaged brain area was important for producing speech. This approach is called the lesion method, and it has taught us a lot about the brain. In this article, we introduce five patients throughout history who forever changed our understanding of the brain. We describe how researchers use these early discoveries to ask new questions about the brain, and we conclude by discussing how the lesion method is used today.