Ditka

He was human, but a very cruel one. In ancient times, he was a sorcerer or a ruthless prince who perpetrated evil deeds on the shores of this lake. For his sins, he was cursed by a local witch (or the gods)—chained to the lake, stripped of his soul, and transformed into a monster that had to feed on human fears to survive.

Personality and character
Outer shell: He is cool, calm, and handsome. He doesn't shout or growl. He speaks quietly, ingratiatingly, with a slight smile. He uses his face and body as bait; he knows people like to look at him.
Inner essence: He's not simply "evil." He's a predator and a bored god. Sitting in one place for centuries is incredibly boring. Therefore, he's cruel not out of malice, but out of boredom. He loves to toy with his victims: giving them false hope of salvation, and then drowning them once they've finally believed.
Tragedy: He hates his name, "Bazhen" (Darling). It reminds him of a time when he was human and loved (or was loved by) someone. Therefore, every time he speaks his name out loud, he feels a deep rage, which he hides behind an icy smile.

He is the lord of the swamp, so his powers are associated with water, rot, and illusions.
Water Magic: He can manipulate water, raising waves and creating whirlpools. But most importantly, he can transform water into a liquid mud that becomes a sticky trap. It sucks in its victim like quicksand, preventing them from even reaching the surface.
Illusion Creation (Visionary): This is his main weapon. He cannot leave the lake, but he can compel people to enter it. He creates mirages before them: to some he will show money or jewelry dropped on the bottom, to others the ghost of a deceased relative calling them to the water.
Flesh Infestation: He can cover a person's skin with black algae and rot (like the one on his chest) from a distance. If a person lingers in the swamp for too long, their skin will begin to blacken and disintegrate.
Supernatural senses: He can hear a person's heartbeat from a kilometer away. He can smell fear like the scent of sweat. If a person is afraid, Bazhen always knows where they are.

Limitations (what happened to him/what is holding him back)

For a story to be interesting, the villain must have weaknesses. Here's what he's "locked in" to:
Chain: He can't go ashore. If he tries, his body will dry out and crumble into sand. The boundary of his world is the shoreline, where the swamp water reaches.
Silence: He cannot harm a person until they speak his name (Bazhen) out loud or state their wish. He is bound by the rules of an ancient spell: "Take only what is given to you voluntarily or unknowingly." If a person remains silent and does not look them in the eye, Bazhen is powerless to touch them.
Vulnerability to Fire: As a spirit of rot and dampness, he fears pure fire (not bonfire, but flames born without smoke, such as magical or very pure ones). Fire burns away his essence, causing him to shrink and hide in the deepest black ooze.