I guess most people interested in sport kites are aware of the Peter Powell Stunter and the Dunford Flying Machine which brought dual-line flying to the masses in the 1970s. But these were not the first kites steerable due to having two lines. In the 1960s, there was the Glite, which, although a single-line kite, included instructions on how to turn it into a steerable dual-liner. And going a bit further back in time, the Target kites date back to the 1940s.
Now look at this, which I recently stumbled across: