A few episodes back on Westworld, Dr. Robert Ford confessed he once had a partner named Arnold. According to Ford, Arnold got too attached to the hosts and attempted to give them consciousness, which led them to believe they were hearing the voice of God, eventually driving them crazy. Ford said that Arnold's obsession with the hosts caused his death in the park, but he was very vague on any other details, leading many viewers to suspect that Arnold isn't actually dead. But if he isn't dead, is it possible that Arnold has been living in Westworld this whole time? It's definitely plausible, but why would he fake his own death just to live in the park?
Well for one thing, Ford could very well be lying about Arnold's death. Bernard was totally unaware that Arnold even existed until Ford used the story about him as a cautionary tale. With that in mind, it's possible that Ford just made the whole story up, or at least the main parts of it. Ford may be very aware that Arnold is actually still out there in the park, though why Ford would allow Arnold to just roam around the park remains a mystery.
Another possibility is that Ford is aware Arnold is still alive, but doesn't know where exactly in the park he's hiding. Westworld is pretty big and it seems with each passing episode we discover new parts of the park. Arnold could be stowed away anywhere inside the grounds and Ford could be none the wiser.
In fact, if Arnold is hiding in the park, he could be the one messing with the hosts. If Ford is to be believed, Arnold wanted the robots to be able to think for themselves and that's what this latest update seems to be doing to them. Dolores and Maeve are both remembering their pasts and what has happened to them before when they were part of different narratives. Dolores, especially, has completely ditched her usual storyline loop, with the help of Bernard, and is acting more and more like a guest instead of a host. She's pushed past her previous boundary of "damsel in distress" to become her own hero and is now looking for the maze, which the Man in Black is looking for as well.
The Man in Black somehow knew about Arnold even though Bernard didn't and this may be a clue that the maze itself actually leads to Arnold. The Man in Black said solving the maze would take the game to a new level and what Arnold was trying to do with the hosts would definitely do just that. If Arnold really has been living in the park, it'll be fun to see what exactly he's been up to all this time and how Ford will react to seeing his old partner again after all these years.