Jakob Nielsen is an author, speaker and consultant in the field of software usability and web applications. He is a co-founder of the Nielsen Norman Group, which conducts research, provides training and offers consulting in the field of user experience. In addition, Jakob Nielsen holds a Ph.D. from the DTU (Technical University of Denmark) in Copenhagen and is regarded as a thought-leader in the field of usability.
As early as the 1980s, Nielsen published numerous essays devoted to the interaction between man and machine. Initially, Nielsen worked on text-based user interfaces for mainframes. He later became involved with Apple's Macintosh and graphical user interfaces.
According to Nielsen, these topics were extremely helpful for later areas of interest, as the first web applications were also text-based in terms of interaction and dialogue. The central topics of his early work were discount usability and improving the usability of online information. . He became widely known for his approach to discount usability. His three main theses are: 
Discount Usability became a movement, as Nielsen counterbalanced the then common expensive quantitative methods. The original motivation for the concept was Nielsen’s smaller, academic budget, allocated to him to perform his research. The approach still has implications that play an important role in software and web projects today. It has influenced values such as return on investment, accessibility and crowdtesting. In addition, Nielsen coined the term "One Percent Rule," according to which only about one percent of an online community actively generate content and a large portion of it just read along.
Nielsen is regarded by many as a pioneer of usability. The concept of discount usability grew out of necessity, but Nielsen later used this principle to achieve business success. In his opinion, the basics of usability have hardly changed: You should concentrate on user centered design and carry out field studies before starting the actual web design. During the web design phase, empirical studies are added, with Nielsen focusing on qualitative rather than quantitative investigations. Each design process should be iterative, repeating itself to make important changes before the launch of software, web applications or apps. 
Nielsen's concepts can also be applied to mobile applications and response design. The user focus takes into account his or her technical circumstances, for example, a much smaller display, and the technical possibilities of smartphones, tablets and other mobile devices. Those who give a high priority to usability should familiarize themselves with Nielsen's concepts.