He was painted as the villain, but the filmmaker has been accused of editing the story to make him look worse than he was. He was definitely a hateable character, but a lot of the details and timeline were messed with.
> "And again, [Mitchell is] not in it much, but when he's in it, he provides enough evidence that the stuff in King Of Kong was not all that fabricated when it comes to his attitude." (35:48.960 --> 35:59.600)
[1] https://soundcloud.com/jimquisition/the-spin-off-doctors-cha...
Not to mention that he cheated and was the villain in reality.