Dr. Quack has yellow feathers and blue eyes, wearing white doctor coat and lives with his wife, Elizabeth Quack and three children. He is shown in later comics with an eyepatch from being injured during a battle when Sonic was in space.
When King Max Acorn was turning into crystal, Dr. Quack devised a Dream Watcher that allowed Sonic to enter King Max's mind to stop King Max from continuing to turn to crystal. The device unfortunately emitted a kind of energy that Robotnik was able to track, thus enabling him to locate Knothole. When his wife and children were captured, Dr. Quack became a pawn in Robotnik's grandiose scheme. Fortunately, the plan was foiled, and the doctor was forgiven for aiding Robotnik given the circumstances.
Dr. Quack was also the one who, with the help of Nate Morgan, developed Bunnie Rabbot's replacement parts that her body's immune system would not reject. Because of this, Bunnie survived, but would never be able to be de-roboticized. Quack was also responsible for treating King Max and Antoine D'Coolette's father, General Armand D'Coolette, for the poison which Patch injected into them. Unfortunately, the General had been injected with too much poison and passed away, although Dr. Quack was able to save the elderly king. He continues to be the main person the Freedom Fighters turn to whenever someone needs medical attention, and now serves as the head doctor of the Tommy Turtle Memorial Hospital.