It was just revealed in Season 1, Episode 9 of Westworld that
Bernard was made in Arnold's image
Now, I understand that there is supposed be a certain level of mystery surrounding Arnold and what he was up to, but why does no one (in-universe) know what he looked like? Arnold only passed away roughly 30 years ago, shouldn't there be other employees who were around from that time, or barring that pictures of Arnold somewhere? Ford is very manipulative and controlling, but he would not be able suppress everything, especially from outside sources like the media. Or was Arnold really that reclusive, that no other photographs of him exist?
I understand that this question is pretty speculative at this point and that it may be answered in the next episode. To prevent closure, I would limit answers to out-of-universe interviews and quotes from the cast and crew if no in-universe answer is available at this time.