While not technically a new character, Westworld introduced the mysterious Arnold to us in the third episode "The Stray." The malfunctioning hosts had been calling out the name "Arnold" and when Bernard asked Dr. Ford about it, he gave us a lot of back story, but still not quite enough to form a complete picture. What ever happened to him? Did Arnold kill himself on Westworld? Something Ford says definitely implies that this is what happened.
When telling Bernard the story, Ford explains that this enigmatic character was once his partner, and helped him in the creation of Westworld as well as designing the hosts. Like Bernard himself, Arnold was obsessed with the hosts' consciousness, and tried to create them to be even more human, an idea that Ford seems to have been not entirely down with. At the end of his life, Arnold apparently lost it a bit, and spent all of his time in the park, speaking only to the hosts themselves. His death within the park was deemed an accident, but Ford seems to not entirely buy it. After all, Arnold was very, very careful. The implication here is that Arnold was eventually driven to suicide by his creations.
We still don't know much about Arnold or his fate, and there is definitely something that Ford is keeping a secret. Theories on the internet abound. Some argue that Arnold is not even really dead. He could be the Man in Black, or he could have been re-born in the form of Bernard, who may or may not be a secret robot. Even what could have driven him to suicide is a bit of a mystery. Was he that heartbroken over the fate of his robots? Ford said that his life was marked with tragedy. Could this tragedy have finally gotten the better of him? Was he driven to suicide by the knowledge that he could never make the robots fully human?
Whatever his fate, it is abundantly clear that dead or not, he is still very much a part of Westworld and everything that goes on within it. The hosts are trying to reach out to him, and Bernard is being positioned as his replacement, whether literal or otherwise. I have a feeling that we're about to learn a lot more about this character, and it's probably not all going to be good.