What created Dark Link, and what is his purpose?

In the Legend of Zelda series, a recurring character that appears in a few of the titles is Dark Link. After reading the wiki a few quotes stand out:

"Conquer yourself" - Navi

Dark Link is never described as one of Ganon's servants; the more likely scenario is that it was a final test left by the King of Hyrule who hid the Triforce of Courage. [The Adventure of Link]

Though in later titles, the appearance of Dark Link just becomes more vague.

Now, we can all agree that Link (aside from an uncontrollable need to destroy all pottery) is a pretty good guy. He'll go to extreme ends just to return seemingly valueless items, just to make people happy, he'll put his life on the line for the defense of others, and above all else, he is the owner of the Triforce of Courage, which certainly says something about his character.

So this could lead to a few outcomes:

1. Due to his squeaky clean reputation (I mean, no one even really seems to care about the pottery anyway), there is a lot missing from his character. Due to some form of outside force, Dark Link was born from this.

2. There are always two sides to a coin. In this case, Hyrule, and Lorule. From the synopsis of A Link Between Worlds:

   The game is set in the two kingdoms: Hyrule, a location used in many past Zelda games, and Lorule, a new kingdom that acts as dark twin to Hyrule

   This seems like the more likely scenario, and much easier to explain, but does this explain Dark Link's re-appearances throughout most of the series?

So where exactly did Dark Link come from, and why does he keep appearing?