The Fast Walker was never a completed model. There were never any pictures of him in game. The only picture of him is a sketch that says he is a a highly intelligent dog like creature that would follow the player, acting like a guard dog, and would eat what it kills. The pic also says that he would run away on sight of a major enemy or important event. He has 6 eyes for nightvision and heat detection and well developed forelimbs for use of machinery and weapons. He either got replaced by the Panther (a never finished character), the Hound Eye, or he was just a never finished character.
The only picture of the Fast Walker