Giles Corey is one of the oldest citizens of Salem.

When he initially appears in The Crucible, Miller describes him as "knotted with muscle, canny, inquisitive, and still powerful."  At 83 years old, Corey is very perceptive about the world around him.  Corey is inquisitive about Putnam's land holdings and his motivations.  He also demonstrates his spirit of independent thought when he asks Hale about the interest that his wife has on certain books.  Corey is a character who is willing to question the world around him.  His inquisitive nature makes him a voice of dissent in a world where such thoughts are being silenced.  

As the play develops, Corey's wife is imprisoned along with Rebecca Nurse and Elizabeth Proctor.  Corey's independent thought is displayed in his assertion that Putnam's motivations are to consolidate his control of Salem real estate.  He proves to be a skilled litigator, challenging the authority of Hathorne and Danforth.

Giles Corey demonstrates one last moment of insight before he is to die. Elizabeth relays this to John in the drama's final moments:

He would not answer aye or nay to his indictment: for if he denied the charge, they'd hang him surely and auction out his property.  So he stand mute, and died Christian under the law.  And so his sons will have his farm.  It is the law for he could not be condemned a wizard without he answer the indictment aye or nay.

Even in his final moments, Giles Corey demonstrates his intelligence.  When Giles Corey is taken to jail and sentenced to be pressed to death, he insists upon "more weight" as his final words.  Giles Corey is Miller's way of reminding the audience that even in the most oppressive of conditions, human beings can display resistance to injustice.