Dissatisfaction with existing games, such as Star Guard and Traveller, and his military experience led to the creation of Space Marines.
[1] Mark was the author of Space Marines and he collaborated with Fitzhugh MacCrae and Bruce Lutz on Gi'ac My.
He met Scott Bizar, the founder of Fantasy Games Unlimited, at Gen Con in 1977, and that meeting eventually led to the sale of the rights for Space Marines to FGU.
Scott Bizar wanted to produce a science-fiction role-playing game, and asked Edward E. Simbalist, Phil McGregor, and Ratner to develop it.
However the collaboration with Mark turned out to be mostly Ed drawing on the material in Space Marines.