It was an engineer in the early 70's for Bally's that conceived of the idea of tying a deck of cards to a random number generator. Bally execs werent keen on the game. They thought it would be a loser.

The first machines were placed in Sam's Town in 1976. It was the 9/6 payscale except the lowest paying hand was two pair. The bank started out getting plenty of action but then it petered out. The main complaint was it sucked down the money to fast.

Someone in Bally's came up with the idea of one pair, jacks of better being the low hand. This brought the RTP up. They put the machines back in and they got continuous action.

At the time Bally had no way of knowing what the RTP was. They paid people to play the game and recorded the results.