Larry Tesler has died aged 74. In the mid 1970s he joined the now famous Xerox Palo Alto Research Center (PARC) to work on human computer interaction (HCI). It is Larry we have to thank for the invention of “Cut, Copy and Paste” techniques in graphical user interfaces - and much more besides.
In 1980 he joined Apple and can lay claim to be a “grandfather” of the Macintosh user interface. During his time at Apple he progressed to become Chief Scientist and was one of the innovators responsible for the Apple Newton PDA that although unsuccessful was ahead of its time. He was also a supporter of the spin-off of Arm from Acorn, another immensely successful development with huge consequences for mobile computing.
Throughout his career he was an evangelist for modeless software: for example “where a user would not have to use a keyboard to switch to a command mode before switching back to edit text. Tesler's vision was that a user's action should have a consistent effect – there should be no "modes" . Hence the cut/copy/paste that we are so familiar with today. In fact Tesler’s personal website is nomodes.com and his car registration was also “Nomodes”. 
Tesler also formulated a HCI truism – the “Law of Conservation of Complexity” which states that “Every application has an inherent amount of irreducible complexity. The only question is: Who will have to deal with it—the user, the application developer, or the platform developer?”
Time and time again the law is shown to be accurate – developers beware!