Rest in peace. It's incredible how young computing is, many of his contributions are so fundamental.
From a guest lecture Larry Tesler gave at CMU in 2014 [1]:
Click to select an insertion point. Double click to select a word. Click and drag to select a passage. All of those were new. Type to replace the selection by new text [...] I think that was not unprecedented, but it wasn’t common. Cut to move the selection to a buffer, Pentti Kanurva had done it, tvedit. Paste to replace the selection by the buffer. Again, Pentti had done that [...] Control B to bold the selection, I and U and so on [...] All of these things were introduced in Gypsy, 1975.
From a guest lecture Larry Tesler gave at CMU in 2014 [1]:
Click to select an insertion point. Double click to select a word. Click and drag to select a passage. All of those were new. Type to replace the selection by new text [...] I think that was not unprecedented, but it wasn’t common. Cut to move the selection to a buffer, Pentti Kanurva had done it, tvedit. Paste to replace the selection by the buffer. Again, Pentti had done that [...] Control B to bold the selection, I and U and so on [...] All of these things were introduced in Gypsy, 1975.
Gypsy: https://en.wikipedia.org/wiki/Gypsy_(software)
[1] https://scs.hosted.panopto.com/Panopto/Pages/Viewer.aspx?id=...