The enemy I hate the most in Zelda 1 is this guy:
He knows you're on a quest to save Hyrule and it's apparently his job to talk to you or something, but he goes out of his way to be as lazy or annoying as possible about it. Sometimes he's even outright hindering.
- He gives you a crappy wooden sword at the start of the game... but only after you bug him. While the sword is helpful, he's really not hurting for resources because...
- He runs the "Money Making Game," an underground gambling ring that extends to several places in Hyrule. He has no problems with robbing the hero blind with it.
- He just flat out refuses to give you better swords despite having them until you have "mastered using them." His measurement of being a master swordsman is really arbitrary since it's not like you can just look at people and say "you have 6 heart containers."
- He has tight control over all the potion shops in Hyrule. The only way to shop at them is through his recommendation.
- He won't let you fight Ganon unless you have the triforce. You could maybe see that as him trying to be helpful by preventing Link from getting slaughtered by Ganon, but alternatively he could be making sure Ganon can pick it up from your corpse.
- There are times where he will block your way and won't let you pass unless you "leave your life or money." That's rather evil.
- He gives cryptic hints with little to no meaning. Sometimes the hints are even flat out wrong.
- He chucks fireballs at Link. I mean it's not Link's fault that his sword slipped and hit the immortal old man.
- You might think that maybe the old man is actually a network of old men, but he runs a network of magical stairs that take you across Hyrule in a flash. It would not surprise me at all if he had many more sets of stairs that he wasn't letting Link use.
- Speaking of that network of stairs, he doesn't tell Link where any of them go, so it's really easy to get lost if you just don't know the logic behind them.
- He makes you pay him money if you destroy some of his secret entrances. He does this knowing full well that the hero has to find secret dungeon entrances so doing this by accident is a high possibility.
- He makes offers where he will only let you have one of two items: a potion or a heart container. Thanks to his tight control of the potion shop network, this is his way of saying you'll have to go to him for potions regardless. Also he throws away the item you don't pick instead of giving both to the hero like a nice person would do.
- Did I mention he's immortal?
- He wears red robes and tries to act as an adviser. You know who else wears red robes and tries to act like an adviser? Jafar.
So yeah. Don't be fooled. The Old Man is definitely a Zelda 1 enemy. 
