Duke was a four year old Dobermann pinscher weighing 23 kilos. Chuck Hooper liked Duke for his energy and cheerfulness. Duke knew what he had to do for Hooper.

Once while jumping he hit Hooper about the belt, causing him to fight to keep his balance. He never jumped on Chuck Hooper again. With Hooper standing, the dog walked to the end of the leash and tugged steadily. Leaning against the pull, Hooper learned to keep his balance. In this way, Duke helped Hooper to go on for short walks.