The Mentor

If there's one thing he doesn't know how to do, it's how to not die.

The one who taught the Hero much of what they know. They're usually much older than their pupil. They also indirectly teach the audience about the world, such as critical historic events, how the world works (if the world works in a way significantly differently from real life), and why certain things are what they are. The Mentor is often an old man who has volumes of knowledge that he hopes to pass down to his student so then they can become as wise or powerful as he is one day. He might've gotten this knowledge from past experience with conflicts the Pupil is currently going through, making him a Retiree Hero.

The general description of the Basic Mentor go as follows: an old man who can often be seen meditating or testing his skills on Practice Dummies. He is a naturally tranquil individual who may be slow to start his Pupil's training, causing them to become impatient and beg their master when their learning will begin. He speaks softly and calmly, only ever raising his voice when the Pupil is being greatly annoying or when trouble suddenly arrives and it's time to fight. The Mentor's way of teaching isn't straightforward, forcing the Pupil to really think about what they're being told to understand their lessons. Even in the face of his enemies, the Mentor is able to keep a composed and polite posture if he isn't currently being attacked. One of the Mentor's goals in his teachings is to not only educate the Pupil on the techniques they want to learn, but also to have them pick up Life Values such as discipline, patience, self-respect, and decency.

As the Mentor and Pupil spend time together, they may form a parent-child-like bond over the course of the Pupil's training. This is what sets up the drama for when the Mentor dies to the Villain or one of their Henchmen. And because of their penchant for death, they're rarely ever around to see the Hero win the Big Fight against the Villain, but they might die once the time for final conflict is near. In some cases, the Mentor will help out in the Big Fight, but might also die in the process. If the Mentor dies, the Big Fight is either in progress and hasn't been started yet, and the Villain or someone close to them is responsible for the death, the Hero will have the urge to avenge their teacher.

Examples of The Mentor
Naruto - Kakashi Hatake and Jiraya. Both serve as Naruto's mentor. Kakashi came first and taught him most of the basics of the ninja world, then Jiraya taught Naruto how to use one of his most important techniques: Rasengan. Unfortunately, later in Shippuden, Jiraya is killed by Pain. But to be fair, that's what he gets for being a Mentor.