The word hero is Greek, from a root that means "to protect and to serve". A Hero is someone who is willing to sacrifice his own needs on behalf of others, like a shepherd who will sacrifice to protect and serve his flock. The root of the idea of Hero is connected with self-sacrifice.
The Mentor: A Wise Old Man or Woman
An archetype found frequently in dreams, myths, and stories is the Mentor, usually a positive figure who aids or trains the hero. Campbell's name for this force is the Wise Old Man or Wise Old Woman. This archetype is expressed in all those characters who teach and protect heroes and give them gifts. Whether it's God walking with Adam in the Garden of Eden, Merlin guiding King Arthur, the Fairy Godmother helping Cinderella, or a veteran sergeant giving advice to rookie cop, the relationship between hero and Mentor is one of the richest sources of entertainment in literature and film.
The word "Mentor" comes to us from The Odyssey. A character named Mentor guides the young hero, Telemachus, on his Hero's journey. In fact it's the goddess Athena who helps Telemachus, by assuming the form of Mentor. Mentor's often speak in the voice of a god, or are inspired by divine wisdom. Good teachers and Mentors are enthused, in the original sense of the word. "Enthusiasm" is from the Greek en theos, meaning god-inspired, having a god in you, or being in the presence of a god.
The Threshold Guardian
All heroes encounter obstacles on the road to adventure. At each gateway to a new world there are powerful guardians at the threshold, placed to keep the unworthy from entering. They present a menacing face to the hero, but if properly understood, they can be overcome, bypassed, or even turned into allies. Many heroes (and many writers) encounter Threshold Guardians, and understanding their nature can help determine how to handle them.
Threshold Guardians are usually not the main villains or antagonists in stories. Often they will be lieutenants of the villain, lesser thugs or mercenaries hired to guard access to the chief's headquarters. They may also be neutral figures who are simply part of the landscape of the special world. In rare cases they may be secret helpers placed in the hero's path to test her willingness and skill.
Often a new force will appear in Act One to bring a challenge to the hero. This is the energy of the Herald archetype. Like the heralds of medieval chivalry, Herald characters issue challenges and announce the coming of significant change.
Typically, in the opening phase of a story, heroes have "gotten by" somehow. They have handled an imbalanced life through a series of defenses or coping mechanisms. Then all at once some new energy enters the story that makes it impossible for the hero to simply get by any longer. A new person, condition, or information shifts the hero's balance, and nothing will ever be the same. A decision must be made, action taken, the conflict faced. A Call to Adventure has been delivered, often by a character who manifests the archetype of the Herald.
People often have trouble grasping the elusive archetype of the Shapeshifter, perhaps because its very nature is to be shifting and unstable. Its appearance and characteristics change as soon as you examine it closely. Nonetheless, the Shapeshifter is a powerful archetype and understanding its way can be helpful in storytelling and life.
Heroes frequently encounter figures, often of the opposite sex, whose primary characteristic is that they appear to change constantly from the hero's point of view. Often the hero's love interest or romantic partner will manifest the qualities of a Shapeshifter. We have all experienced relationships in which our partner is fickle, two-faced or bewilderingly changeable.
Shapeshifters change appearance or mood, and are difficult for the hero and the audience to pin down. They may mislead the hero or keep her guessing, and their loyalty or sincerity is often in question. An Ally or friend of the same sex as the hero may also act as a Shapeshifter in a buddy comedy or adventure. Wizards, witches, and ogres are traditional Shapeshifters in the world of fairy tales.
The archetype known as the Shadow represents the energy of the dark side, the unexpressed, unrealized, or rejected aspects of something. Often it's the home of the suppressed monsters of our inner world. Shadows can be all the things we don't like about ourselves, all the dark secrets we can't admit, even to ourselves. The qualities we have renounced and tried to root out still lurk within, operating in the Shadow world of the unconscious. The Shadow can also shelter positive qualities that are in hiding or that we have rejected for some reason.
The negative face of the Shadow in stories is projected onto characters called villains, antagonists, or enemies. Villains and enemies are usually dedicated to the death, destruction or defeat of the hero. Antagonists may not be quite so hostile---they may be Allies who are after the same goal but who disagree with hero's tactics. Antagonists and heroes in conflict are like horses in a team pulling in different directions, while villains and heroes in conflict are like trains on a head-on collision course.
The Trickster archetype embodies the energies of mischief and desire for change. All the characters in stories who are primarily clowns or comical sidekicks express this archetype. The specialized form called the Trickster Hero is the leading figure in many myths and is very popular in folklore and fairy tales.
Source: The Major Archetypes