Darknut

Darknuts are a long-time Zelda enemy, having first appeared in The Legend of Zelda. Darknuts seemed to have been ranked by Ganon, and different ranks wore different amour and carried different weapons. Regular Darknuts wore grayish armor, sported a Viking-like helmet, and carried only a sword. Red Darknuts, otherwise known as Mighty Darknut, showed their higher rank via crimson armor, a crimson cape, a helmet that covered the entire face, and a crimson and yellow shield with their serrated swords.

The Legend of Zelda
In The Legend of Zelda, the armored Darknuts are part of Ganon's elite fighting corps. They were some of the toughest enemies around, being equipped with shields that repelled all frontal attacks, doing a decent bit of damage, having plenty of stamina, and having an unpredictable movement pattern. They appeared in most dungeons, and normally in multiple numbers, increasing their threat even further.An Easy way to get rid of them is with a bomb.

The Legend of Zelda: Oracle of Seasons and The Legend of Zelda: Oracle of Ages
After a long absence, Darknuts reappeared in The Legend of Zelda: Oracle of Seasons and The Legend of Zelda: Oracle of Ages. They behaved similar to their The Legend of Zelda counterparts, but were much weaker, as their attacks didn't do as much damage and they could be hit from the front

The Legend of Zelda: The Wind Waker
These armored knights reappeared in Legend of Zelda: The Wind Waker, where their strong armor and massive blades proved a formidable match for Link. The Darknuts were also extremely resourceful and would engage in hand-to-hand combat without a weapon or take advantage of fallen enemy's weapons if it had lost its own. Weak when attacked from behind, where their armor was strapped, Darknuts in this game had relatively few other weaknesses. Link soon discovered that the best way to deal with these powerful enemies was the Parry Attack, which would allow him to easily remove the Darknut's helmet or armor and avoid its sword. Finding a Darknut normally means the presence of the enemy scenario.

Multiple Darknuts
Encountered in later dungeons and in the Savage Labyrinth on Outset Island. While it may seem that multiple Darknuts pose a greater threat than one, the battle is essentially the same. Picking them off with Link's parrying attack and the player keeping his or her guard up still works. It is assumed, however, that by the time the player encounter more than one Darknut, he or she will have a decent amount of hearts and the higher number should not pose a real threat.

The Legend of Zelda: Twilight Princess
Darknuts in The Legend of Zelda: Twilight Princess are much harder than in The Wind Waker. They start out with armor, a large sword (or mace), and a shield. When Link lands a hit on them, some of their armor comes off. Eventually their shield will fall too. After being stripped of all their armor, they will throw their large sword or mace at you. At this stage they use a smaller sword and wear only their under-armor chain mail making them much more agile. One Darknut is the mini-boss in the Temple of Time, while others commonly guard items such as keys or new parts of an area. In some cases Link fights multiple Darknuts at a time which can be overwhelming. Also, They can have different attacks: vertical and swing attacks with their first weapon. The thrusting and cutting attacks with the small sword.

The Legend of Zelda: The Minish Cap
In The Legend of Zelda: The Minish Cap, Darknuts returned again, this time with a Darknut who was even stronger than the Mighty Darknuts. This one was known as the Black Knight, a Darknut resembling a regular Darknut, only instead with a shield and cape. Everything about it was black as midnight, and it challenged Link as the mini-boss of the final dungeon in the game, Dark Hyrule Castle.

Quote from The Legend of Zelda: The Minish Cap Dark Nut figurine:

"Appears in Dark Hyrule Castle. These armor-clad soldiers are tough. Use your shield and rolling skills to find an opening in their defenses!"

(See also: Mighty Darknut)