Via Starwars.com:

The Mentor (or wise old man/woman) is one of the more recognized archetypes of mythology for a good reason. While most people are aware of what a mentor is, there are deep origins to the word worth exploring.

Definition: The Mentor

The mentor is a guide for the protagonist, and is often seen giving them advice and sometimes gifts. They can be a parent, grandparent, friend, coach, or teacher. They are often mystical or foreign in origin — sometimes portrayed as a wizard — and can take many forms, including dark, fallen, and comic.

Despite the fact that mentors are so important in the lives of our heroes, they often disappear partway through the story. This is likely because a hero must stand on their own to complete their journey. A mentor helps at the beginning, but the full development of the hero is not achieved until he/she leaves.

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