The first standard Unix text editor that we used was ed which was based on QED, see also An incomplete history of the QED Text Editor. William Newman had already written a version of QED for our older Interdata/MIFS computer systems.
Let Richard and Harold tell you about ded in this PDF The life and times of ded, text display editor. Jon Rowson wrote a 19-page introduction to ded and em in the QMC Unix Papers. This full-screen display editor needed a so-called Visual Display Unit such as the ITT 3210 VDU Terminal and the Hazeltine 1510 VDU Terminal.
Having used ded I was not impressed when I used vi for the first time at Bell Labs. I suppose one never forgets how to use the first editor that one has mastered; I can and do use ed from time to time, especially in shell scripts. So excuse me when I say in the year 2013 2021 that there are two things that you need to know about vi (and emacs):
Note for Betonköpfe: the use of vi, vim or vile is inexcusable.