This underplays his contribution to our situation today. He was all about modeless computing which meant you no longer had to get into a mode to do edits and so forth. Things were done inline.
He also lead the milestone tour of Xerox PARC for Steve Jobs and his team which planted the seeds for how Macintosh operated and seeds for what NeXT would do when Steve was exiled by Apple.
Tesler later moved to Apple as chief scientist. In the nineties he advised CEO Gil Amelio to choose NeXT over Be Inc when searching for a modern operating system to replace their failed projects at Apple. He infamously warned Gil whichever choice he made meant bringing someone in who would take his job. That lead to Steve Jobs’ return to Apple and consequently Mac OS X and the path to iPhone, iPad, Apple Watch, etc.
PING!.......................
another interesting telling of the Jobs visit to PARC...
https://www.newyorker.com/magazine/2011/05/16/creation-myth