Doctor J is the Gundam Scientist from the L1 Colony Cluster who designed the Wing Gundam. Easily recognizable by his robotic arm and goggles, Doctor J is probably the most frequently seen of all the Gundam Scientists.
Professor G is the Gundam Scientist from the L2 Coloney Cluster. Has has a shaggy mop of hair with a large white nose protruding out of it. An expert in stealth technology, Professor G created Gundam Deathscythe. Duo Maxwell is the former student of this sometimes-mad scientist.
Doctor S is the Gundam Scientist from the L3 Colony Cluster who is renowed for his fake nose. (Why? Don't ask...I don't know.) Even though he created the Gundam Heavyarms, ha had nothing to do with the training of Trowa Barton.
Hailing from the L4 Colony Cluster, Instructor H is perhaps the one and only normal-looking Gundam Scientist--as normal as a mad scientist can get, anyway. Instructor H is responsible for the Gundam Sandrock and the training of Quatre Winner. He's also the one who saved the plans for Wing Zero.
The final Colony Cluster, L5, provided a home to the strong, silent Master O. Master O is recognized by his extremely large stature and bald head. Master O created the sleek Gundam Shenlong and is responsible for the training of its pilot, Wufei.