A Mark 4 Hydraulic Hybrid was a robot.
The Eleventh Doctor and Amy Pond saw one of these robots in the junkyard of Scraptown. The Doctor told Amy that he hadn't seen one of these in years. Then he repaired the robot by reassembling its computer chip. The Doctor called it a beautiful peace of engineering. Later he said that he didn't know what the point of it was, but that he also wasn't sure if engineering needed a point. (GAME: Evacuation Earth)