Who are the important characters in The Canterbury Tales?

Because The Canterbury Tales consists of a series of stories narrated through the voices of various pilgrims, the answer to your question is complicated.
First, I will list the most important pilgrims in the story who narrate their tales in the order in which they appear: Knight, Miller, Reeve, Cook, Man of Law, Wife of Bath, Friar, Summoner, Clerk, Merchant, Squire, Franklin, Physician, Pardoner, Shipman, Prioress, Sir Thopas, Monk, Nun’s Priest, Second Nun, Yeoman, Manciple, and Parson.
In addition to the pilgrims, the Host is a major character since he is the one that suggests the storytelling contest in the first place. The narrator is also an important character since he is the one that characterizes the pilgrims in the General Prologue.
Within the stories themselves, there are a few characters who stand out as important.
In “The Knight’s Tale,” the main characters are Theseus, his father Egeus, the prisoners/brother’s Palamon and Arcite, and Emelye, the maiden both brothers desire.
The “Wife of Bath’s Tale” includes a brief discussion of her five husbands before launching into the story of King Arthur’s knight and the old woman who is actually a beautiful maiden in disguise.
In “The Nun’s Priest’s Tale,” the narrator tells the allegorical story of Chanticleer and Pertelote, a rooster and hen who are husband and wife. Chanticleer is caught by the Fox, a stand-in for evil in the story.
While there are other characters within the pilgrims’ tales, these are the ones that stand out the most.