Of all the bosses in Metal Gear history, there is none less intimidating than The End. The first time this old man is introduced, he is sat in a wheelchair barely able to function, and then he gets carted off before he really gets a chance to do anything.
After battling two other members of the Cobra unit - one who is basically Predator-lite and another that controls literal bees - it's a bit disappointing to be fighting an old man who can hardly get out of a chair.
Then, the player has to sit and watch as he tranqs Snake over and over again; all the while managing to sprint at breakneck speeds and recover energy from the sun itself.
The resulting boss fight is one of the most fun and challenging in the entire game, as the player is drawn into a game of cat and mouse, slowly hunting the old sniper through the thick jungle as he does the same to you. The only difference is that he's better at it.
So when the player finally hunts him down after so much gruelling attrition, it really is a lesson in never judging a book by its cover.