Going back from Seoul 1988, here is a video about the individual dressage competition from Los Angeles 1984 (it also includes a brief overview of the earlier Olympics).
And here is Reiner Klimke performing his now legendary victory lap. For some context: video starts with Klimke asking the horse for some 60 flying changes, with one hand, and on a curving line. That just shows incredible harmony that Klimke had with Ahlerich. It's essentially the easiest dressage move to mess up - even today, a lot of riders lose rhythm while performing only 15 flying changes, on a straight line, and with both hands in a competition.
Fun fact: this is also how freestyle competition got invented. Klimke was doing this while John Williams' Olympic theme was playing in the background. It inspired officials to invent the freestyle to music competition, which would eventually join the Olympic program in 1996.