Jakob Nielsen is a prominent web usability expert known for his work in improving user experience on websites. He co-founded the Nielsen Norman Group, a consulting firm that focuses on user-centered design and research. Nielsen is widely recognized for his principles of usability, which help designers create more effective and user-friendly interfaces. Nielsen is also famous for his "10 Usability Heuristics for User Interface Design," which serve as guidelines for evaluating and improving the usability of software and websites. His contributions have significantly influenced the fields of human-computer interaction and user experience design, making digital products more accessible and enjoyable for users.