Ganon
From Hyrule
"We shall truly see which is more worthy of being feared: the Deity of Time, or the Deity of Evil."
"You still call yourself by that ridiculous title? You are no god."
"Or perhaps I am, and you just have not come to realize it yet."
-Ganon and Aalya, Force of Gold 9 - Beasts of War
Ganon is the main antagonist of the Zelda series and is a constant threat to Hyrule and its citizens. Though he is dead, he is still well-known in the Zelda world, his army of darkness still roams the land, and he is still a danger to Hyrule through his ability to speak to and influence living Hyrulians. He is commonly depicted as a large, pig-like beast in stories and pictures, though there is debate over which of his two forms, two-legged or four-legged, is his true visage.
Known history.
The history of Ganon, much like the history of Hyrule, is hard to discern and make sense of. However, much of his past is known still.
In the original kingdom of Hyrule, countless years ago, Ganondorf Dragmire, who was the current king of the Gerudo tribe, heard of a great power--the Triforce. He created a plan that would allow him to obtain it, and it mostly succeeded. He acquired the Triforce of Power, and led Hyrule on a path of destruction for seven years. Then, the Hero of Time, Link, appeared, and waged a great battle against Ganon, and the dark beast was vanquished.
Not all was over. Through time manipulation, Link set things right, but years later, Ganon returned, and waged an incredible war on Hyrule. The land was drowned under water by the three goddesses, who saw what a threat Ganon was. The dark king was trapped.
Many years passed, and he broke free from his imprisonment underwater, and began a search for the other Triforce pieces. during the search, his servant, the Helmaroc King kidnapped a young girl named Aryll, the younger sister of a new Link. This Link set out, and with great effort, battled Ganon again, imprisoning the beast under water once more.
Even more years passed, and eventually, New Hyrule was discovered and founded. Many years passed, and Ganon appeared again for the last time, seizing hold of Hyrule. Again, a hero named Link appeared to stop him, and he vanquished the giant pig, hopefully once and for all.
In HA2 and Backstory
As of Alpha's Force of Gold 9, it has been revealed that Ganon was actually in command of a great many resources during his last attempt and conquering Hyrule, secretly leading the Criminal Underground and commanding a host of mercenaries and assassins, along with many traders and suppliers who had been unaware of their true employer. One of these assassins was Wraith. After the man refused to carry out one of his assignments, Ganon himself cursed Alpha with the scar he carries to this day. Alpha fled the Underground not long after that, being hunted down by many of the beast's minions, who only gave up when news of Ganon's death reached them.
Six years later, at the beginning of HA2, Ganon began to secretly use the scar to influence the Sheikah's minds in subtle manners - never too forcefully, lest he be discovered and recognized as a foreign presence. In FoG 9 it was revealed that his goal appears to be to somehow merge with Alpha in order to regain a physical presence. This goal, while not having succeeded yet, remains an ever present, yet still unknown, threat to the entirety of Hyrule.