He also worked for the Fenwick rod company, testing out new rod models, helping in the design of the rods, & giving them his valuable feedback of the rods they made. He was actually the inventor of their famous Feralite ferrule.
As a casting instructor there may not have been any better than Jim Green. Below is a video (shot on 16 mm film) Jim made back in 1975 for the Fenwick company. In it he describes & shows the basics of good fundamental fly casting. This is probably the best, most straight-forward, easiest to understand casting instruction I've seen. It's about 23 minutes long, but worth watching every second of it. Expand the player to full screen mode to get the most out of it. In fact, you'll want to take your rod out on the lawn for a while after watching this video & come back & watch it again & again.