William is in face the MiB. There's lots of evidence for this both thematically and evidently. William and MiB are following opposite character arcs, William growing more in love with the park, MiB more disillusioned. MiB seems to be referencing events in William's storyline like the Ghost Nation fight, Lawrence. I also believe that Bernard is in fact Arnold and his talks are in fact thirty years prior to MiB's storyline. Here is where my conjecture takes over. Arnold, through his talks with Dolores is attempting to create sentient life. In fact, the security guy uses the exact same questions early in the series as a diagnostic. That tells me that Arnold's line of questioning did in fact foster sentience. Later on, these questions are used as a diagnostic to know if any of the hosts are becoming sentient. If they are, they are decommissioned. I would suspect this is a protocol instituted by Ford as he believes the hosts are nothing but dolls and cannot think or feel, contrary to what Arnold believed. William falls in love with Dolores. They go on an adventure, and perhaps Dolores achieves true sentience. The park finds out and has her mind wiped. In the intervening thirty years, MiB/William returns frequently to the park to try and break Dolores out of her loop so that they can be together. He mentions that when they (host/guest?) are suffering that is when they are their true self. So in a bizarre way he keeps running through her loop and torturing her to get her to remember every iteration.