Georg Cantor was a German mathematician best known for founding set theory, which revolutionized the way we understand infinity and the concept of numbers. His work introduced the idea of different sizes of infinity, demonstrating that some infinities are larger than others, a concept that was both groundbreaking and controversial in his time. Cantor's theories laid the groundwork for modern mathematics and have had a profound impact on various fields, including logic and philosophy. Despite facing significant opposition from some contemporaries, his ideas eventually gained acceptance and are now fundamental to mathematical thought.