professional, although he prefers, and coined, the term "interaction designer
Author of the books About Face, widely considered a classic in the field, and its corresponding business-case book The Inmates Are Running The Asylum. Founder of Cooper Interaction Design, a Palo Alto-based consulting firm. More recently, he's renamed his firm to Cooper Methods and moved toward more abstract corporate consulting.
Creator and programmer behind many of the original concepts of Visual Basic. He called it Ruby before he sold it to Microsoft, and Ruby is now the name of an unrelated programming language.
The crux of Cooper's design approach, and what distinguishes him from most of his peers in the field, is his focus on the user. That's an admittedly odd statement to make about user interface professionals, but so many of the leading lights in UI seem to fixate on a particular idea or interface structure that they feel will revolutionize the industry and make everyone's lives easier, if only tech companies would adopt it. David Gelernter's Lifestreams project comes to mind, as do large parts of Jef Raskin's book The Humane Interface. They remind one of the science professor from Ninja High School, running around yelling, "The world can be saved by steam!" to anyone who will listen.
Cooper is a little more flexible. By focusing on understanding the user and his or her goals, rather than developing a catch-all solution, Cooper provides a methodology that helps designers do what's appropriate for this particular class of user, this particular application. Cooper's firm even recommends inventing fictional personas to represent the target user, going so far as to give them names and stock photography headshots.