I can only speak for myself here, but, to me the thing that really defined Traveller when I first laid my hands on it, were Dietrick's pieces in the old Traveller Book. Shawna, Jameson, the cover art on the Starter Traveller box, really defined the futuristic and yet very tangible feel and look for the game. He is essentially part of the reason I latched onto this. He did some work for other games, notably another cover of his I really like to this day, is the one he did for the old "Trailblazer" game by Microgames.
https://68.media.tumblr.com/a9f58b4be763737a3d0f5097bc0b74cd/tumblr_od71om6nCY1ro2bqto1_500.jpg
It's my opinion that his clean lines and ability to abstract and create a single piece visual montage or tapestry. The guy on the cover of the Starter Traveler box is some tall typical blonde dude from the 70s with feathered hair. Him holding his helmet and staring out at the buyer or owner of the box, while two familiar people in the background face off in two different directions, really speaks to adventure and the adventure spirit of not just this game, but the scifi genre as a whole.
I just wish he could do massive amounts of art for not just Traveller, but all games and scifi books.