Some info I found
"So where did the modern compound bow come from? American ingenuity, that’s where. In striving to make a better bow a gentlemen in the early 1960s came up with the idea of using pulleys to improve performance. At this time American was experiencing a surge of interest in outdoors activities and particularly bow hunting. With so many Americans absorbed in this aspect of the sport, it was not surprising that someone started experimenting to improve the efficiency of the bow.
Fred Bear had begun to improve bows with new materials and designs but one man changed the way we would bow hunt forever. A mechanic from Missouri called Howless Wibur Allen. Early in 1961, he was inspired by the launch of the Hoyt Pro Medallist. This was one of the first bows designed with stabilizers. Allen thought that he could further enhance the performance of the archery bow by using another ancient invention; the wheel. Allen’s brilliant idea was to harness the block and tackle principal of a pulley to a bow. In this way he reasoned that the mechanical advantage of the pulley should enable a heavier weight bow to be drawn.
He created his first experimental bow by sawing off the limb tips of an old recurve and attaching small pulleys to it. The resulting bow had a very short draw-length as he had used conventional, center axle pulleys. However, Allen did not give up but continued to experiment with different pulley systems. The most successful arrangements included cam shaped wheels and round pulleys with offset axles called eccentrics. These methods not only provided a more usable draw length but also resulted in an enormously beneficial side effect. The bow reached its peak weight at mid draw then reduced to a much lighter weight at full draw. This enabled Allen to comfortably hold at full draw, a heavy weight bow. When he tested these bows, Allen discovered that they had a really excellent cast and a surpassingly flat trajectory. After he refined his new bow, H W Allen filed patent application number 3,486,495 on 23rd June 1966 for an "Archery bow with draw-force multiplying attachments" and the compound bow was born."
Taken from another site