This is my current, over-romanticised plan for how my life should unfold, but won't, because it's only the way things work in fiction:
Hero Senior and I are buddies. He is by far the dominant partner, I am more of a sidekick. We engage in minor heroics, and generally have a grand old time. We are extremely close. Nothing can come between us. Until something does. Well, two things, actually.
The first is a girl. Suddenly Hero Senior starts paying more attention to this girl than he does to me. It annoys me. Much. No girl distracts my attention; I still pine for the one long lost. But Hero Senior starts to want some time away from me, some private time to woo his lady, or some such. I am most jealous. I am left to my own devices, and know not how to use them.
During some of my newfound time without direction or object, I meet someone new, who happens to be the second thing that comes between me and Hero Senior. Someone very charismatic. A bit older than me or than Hero Senior, he has not only seen the world, but experienced it. He has plans, grand plans, not just the petty heroics in which my good buddy and I used to engage. And I can help him carry out those plans, he says. Soon I am spending more time with him than with Hero Senior. For some reason, I never tell Hero Senior exactly what I have been doing without him, or who my new friend is. By the time of the marriage between Hero Senior and his sweetheart, I scarcely care about him anymore. I belong to this charismatic person now.
Naturally, this charismatic person is the Villain of the whole thing. And I am his principal henchman, most devoted. I love the Villain. My loyalty is to him, not to his cause, but to him alone. But he, being a Villain and all, is not so susceptible to love. Love is a weakness. To him I am nothing but useful, he cares nothing for me.
At some point he proves this. I know not how, perhaps he shows himself too willing to sacrifice me for his cause, perhaps he refuses to spare the life of my long-lost love, perhaps something else entirely. In any case, I am deeply hurt, and leave his service and his fealty. I retreat into a long exile somewhere, doing something very much alone.
When at last I emerge from my decades-long sulk, I find that the Villain has gained great power, and in doing so killed Hero Senior and his wife, who dared oppose him. Their son, the Hero, has grown up in the care of some obscure relative, an uncle, probably. And, naturally, he being the Hero and all, it is his destiny to defeat the Villain and restore the world to right.
By this time I have gained quite a bit of wisdom and badassitude alike. That's what happens when you work for a villain for years and then go live in exile doing something exile-ish for years more, you know. I cannot defeat the Villain myself, I am too old and emotionally weak. Yup, you guessed it, I am now the Mentor. I gain the Hero's trust, take him under my wing, impart as much as I can (though nowise all) of my wisdom and badassitude to him, and set him on his way to saving the world.
And, thanks to the occupational hazards of being a Mentor, before the Hero accomplishes his destiny, I die. In some noble, Mentor-worthy way. Probably killed by the Villain himself, or else by his primary subordinate. But my death in some way advances the cause of the Hero, and I know that the side of good will ultimately triumph, because this is the archetypal hero-journey cycle, after all.
So, I'm dead. And the Hero goes on and defeats the Villain. Yada yada.
See? Never going to happen. We don't have clear-cut heroes and villains and mentors out here in the real world. We don't have the archetypal hero-journey cycle. Make a nice book, though. Bit of a twist on the same old story - not much of a twist, really, but even so. Focus on the Mentor 'stead of the Hero. Meh.