Stalfos

The Stalfos are skeletal knights that have challenged Link since the original The Legend of Zelda.

In The Legend of Zelda
Stalfos appear only in the first and seventh dungeons and are skeletons carrying swords in both hands. Though they are usually found in large groups, they are easy to defeat and do little damage.

In The Adventure of Link
Stalfos can be found in palaces throughout the game in three varieties: normal, red, and blue. Normal Stalfos are white skeletons with swords and shields and are considerably weaker than red and blue Stalfos, which have more skills and can jump and perform thrusting attacks.

In A Link to the Past
Again, Stalfos come in three forms, normal, red, and blue. Red Stalfos can throw bones at Link while blue ones jump around to do battle. There are also Stalfos Skulls, which are more difficult to beat and, in some cases, invulnerable. 

In Ocarina of Time
Stalfos carry around a sword and shield and are a common enemy found in several temples after Link becomes an adult. They can perform sword slashes and overhead jumps and are able to block Link's attacks effectively. They will occasionally come in pairs. If this is the case, it may be that if Link defeats the first one but takes too long to defeat the second one, the first one will be revived, forcing Link to fight both again. Whether or not the remains of the first Stalfos disappear will tell Link if he needs to destroy the second one quickly.

They serve as a mini-boss within Ganon's Tower and are found in the room with the boss key. In addition, Link will have to fight off two of them while attempting to escape from the castle with Princess Zelda.

In Majora's Mask
Part of the Ikana race, Stalfos keep guard over King Ikana. They appear in this game only as a mini-boss.

In The Wind Waker
Stalfos are large skeletons carrying spiked clubs as opposed to the usual sword and move very slowly. They come out of coffins and the ground and can be defeated with a combination of bombs, the boomerang, and Link's sword. If Link breaks the Stalfos apart but does not destroy it in time, it can reassemble itself. Using the Skull Hammer after breaking it apart will kill it in one hit.

In The Minish Cap
Stalfos can be found in the Fortress of Winds, Dark Hyrule Castle, and the like. They often disguise themselves as normal skulls, but when Link gets close, they pop out and attack him.

In Twilight Princess
Stalfos are only found in the Arbiter's Grounds, the Cave of Ordeals, and a secret grotto. They wield short swords and either wooden or metal shields. The ones with wooden shields can be disarmed while the ones with metal shields cannot. After they are broken to pieces using Link's regular attacks or hidden skills, they can reassemble themselves; to prevent this, plant a bomb on their remains. The Ball and Chain also works effectively on them once Link acquires it as an item.