Giles Corey is a very unique character, and we are introduced to him first in act one. He is good friends with John Proctor, and they leave together at the end of the act. You will learn more about his unique traits as the play progresses, but in act one we learn several things about him that make him unique, and stand out from the rest of the people there.
First of all, he is an older man who speaks his mind quite plainly. He has also sued many of his neighbors for various offenses. He even sued his good friend John Proctor for "sayin' [he] burned the roof off [his] house." John asserts that he never said any such thing, but paid the court fees anyway. Giles seems to be a grumpy, cantankerous old man that people are highly amused by, and put up with. So, the fact that he sues people a lot is definitely a unique trait. Another unique thing about Giles is that he got married for a second time later on in life, and is baffled by the fact that his new wife likes to read books so much. In fact, he is almost convinced that her reading books has to do with the fact that while she is reading, he can't say his prayers, and he brings this interesting fact up to Reverend Hale. Unfortunately, that information later lands his wife in jail, accused of witchcraft. He regrets saying anything about it, and goes to the courts to try to save her.
Corey, in the end, ends up being a unique hero in the course of the play. His rather funny character traits turn very serious as he stands his ground on moral issues, and he proves to be one of the best of them all. I hope that those thoughts helped; good luck!