The Trecherous Advisor of Argus: Sorcerer Hein

Hein was once the loyal advisor of King Argus, until the Great Earthquake hit the Floating Continent. Darkness consumed Hein and granted him great power at the cost of making him power-hungry. To that end, he brainwashed Argus' men into serving him, imprisoned those he could not as well as the king, abducted the Elder Tree from the Living Woods, turned it into his fortress, and lastly sent his new soldiers to pillage the town of Tokkul.

Hein's a busy man.

Hein is quite the villain by Final Fantasy III standards. He's the final boss of the Floating Continent and is built up accordingly: The party learns what he's up to while they're traveling with Desch and his castle can be seen floating in the desert near Tokkul. The remake even adds various new scenes of the party reacting to the problems of Argus, the Living Woods and Tokkul. Still, it's only after the heroes have been blessed by the fire crystal and a man begs them to stop Hein's minions from burning down Tokkul do they finally take the fight to him.

Hein is one of Final Fantasy III's more memorable villains. In addition to the tried and true crowd-pleaser of "Skeleton", Hein has a memorable design and his Barrier Shift makes for a memorable gimmick. On top of that, Hein is the final boss of the Floating Continent, being the last threat the Warriors of Light face before venturing to the surface. In the 3D remake, this also includes a rather significant (yet, not significant) plot dump.

Perhaps for this reason, Hein has gotten some standout treatment over the years. In Record Keeper, he is featured in the Record Dungeons: The more story-focused mode where Tyro and the other RK original characters are experience moments from various Final Fantasy stories. Hein was featured as a playable vision in Brave Exvius, alongside Xande and the Cloud of Darkness for III's villain roster. And finally, both VIII and XIV have characters influenced by Hein (or his Eureka counterpart, Amon), with significant world-building roles.

Overall, Hein is arguably one of the most well-known villains in III.

Battle

Hein is fought at the end of his titular castle. Hein's Castle is unique in that the method of entering is via the party getting paralyzed and sent to the castle as slaves. This means that, upon entering, you cannot leave (although there is a healing spring back at the entrance - granted, you'll need mini to escape the cell, wasting a white/red mage cast).

Hein's signature ability is the Barrier Shift: His weakness defaults to fire, but with the Barrier Shift, he can change his weakness to either Ice, Lightning or Fire. The game doesn't say what Hein's weakness changed to and his evasion is high enough that fighting physically is a toss-up. As even the game tells you, this is the point to use Scholar as their abilities can let them view Hein's weakness. The remake sweetens the pot by throwing in the ability for the Scholar to double the power of items they use in-battle. If done correctly, a Scholar can theoretically defeat Hein immediately, or at least put him at death's door.

However, these are far from the only options. Hein can be brute-forced, either by switching up casts (although be careful as Hein can heal off of absorbed magic) or continuing to fight physically (Hein has high evasion, but can never the less be beaten through basic attacks).