From: Al Kossow 
  https://en.wikipedia.org/wiki/WYSIWYG
 As it relates to computing, there are multiple claims to first use of
 the phrase:
 In mid-1975, John W. Seybold .. and researchers at PARC, incorporated
 Gypsy software into Bravo to create Bravo 3, which allowed text to be
 printed as displayed. Charles Simonyi and the other engineers
 appropriated Flip Wilson's popular phrase around that time. 
 
I looked in the Bravo section of the Alto User's Manual (September 1979), and
in the "Look hardcopy" section (pg. 38), which describes how Bravo can put the
text on the screen almost exactly as how it will appear when printed ("by
positioning each character on the screen within one-half [pixel] of its
position in the final hardcopy"), but I see no reference to WYSIWYG there.
So it must have gotten that tag later. Probably the best way to track the
etymology on this is to look in NewNews archives.
  The phrase was coined in 1982 by Larry Sinclair, an
engineer at
 ... ("Triple I") to express the idea that what the user sees on the
 screen is what the user gets on the printer 
This exact idea existed in Bravo some years before (see above), and was well
known.
  From: Tony Duell 
  a very similar phrase ('What you see, you
get') was used by a camera
 manufactuer some 15 years earlier (at least) 
Yes, but I'll bet Flip Wilson never read any of their ads! :-)
(And I think one can be pretty safe in saying that it was his use of the
phrase that made it popular - at least, in the US. Not sure if the FWS was
picked up on any British channels.)
        Noel