Thomas Deer is a cultural liaison officer at the Kahnawake Language and Cultural Centre. He helped Ubisoft out on Assassin's Creed III, and did one hell of a job making sure it became easily the best representation of Native Americans in a video game.
According to this report in the Montreal Gazette, Deer "was brought on board fairly early in the process of fleshing out the game", and was responsible for overseeing the implementation of a culture often overlooked, if not presented inaccurately, in modern media.
This job meant overseeing the way Ubisoft's developers were handling the inclusion of Native American tribes in the game, but Deer says he stepped in directly on two matters, one which impacted gameplay, the other a little less direct.
The first was scalping. It was originally going to be a part of the game, a seemingly obvious one given the practice's awareness in Western culture, but once Deer says he pointed out that the Mohawk people in question didn't actually scalp (Connor/Ratonhnhaké:ton's people are Mohawk, part of the larger Iroquois confederation), it had to go.
Note: this seemingly contradicts statements made earlier in the game's development, where it was said scalping was cut because it felt "too brutal".