There was never any formal relationship between Sierra and Infocom. Our staffs were friendly with each other, and I hung out with their senior management from time to time, but we were never connected in any way.
It has been 30 years, so my memory is somewhat cloudy on all of this.. but…
My recollection is that they were slightly ahead of us in the market, and had the early momentum. At one time they were on top of the world, and considered us a minor annoyance. I recall them once having something like six of the top ten products. We loved their games, and thought their success was well deserved.
They received perhaps more recognition than us, in the academic world, because they did games that were arguably less mass market and more cerebral. They used words, and we used pictures. Ultimately, we did grab all the marketshare, but it’s really not as simple as that.
Infocom’s management wanted to make accounting software, not games. While we were pushing hard to do better and better games, they were downplaying games to focus on their business software (I forget the name of it). They took their eye off the ball, and we grabbed their customers. The business software, and its failure, crippled Infocom, and I don’t remember them really being a force after that. Lucasfilm gave us much more competition in the years that followed.
I may remember more if you freshen my memory…