Zen-Aku

Zen-Aku is a Wolf Duke Org who had manifested from the Guardian Merrick Baliton, when the latter needed the former's mask to defeat the original Master Org 3,000 years ago.

Biography
No one knows much of Zen-Aku's origin, only that his Org spirit was locked within an evil Wolf Mask. When Merrick's friend Animus had perished at the hands of the original Master Org, Merrick made the decision that he had to stop their enemy once and for all. Heading into a temple, he'd found the Mask of Zen-Aku, put it on, and used his Predazord to destroy the evil Master once and for all.

However, after Master Org was defeated, the Wolf Mask had seized control of Merrick's mind, turning him into (or merging him with) the evil Zen-Aku. While he still had some of his humanity, he implored his fellow Animarian Guardians to destroy him, but they refused and instead used their Crystal Sabers to seal him away in an underground coffin.

Curse of the Wolf
For 3,000 years, Merrick, now Zen-Aku, remained in stasis until the Master Org of the present-day summoned a General Org named Nayzor, who released the Duke Org on the present-day Guardians of Animaria --- the Wild Force Rangers. Though he had no any memory of his former life, he knew that he wanted revenge on the Guardians who sealed him away 3,000 years ago, and he tried to take it by capturing the Rangers' Wild Zords and turning those he captured against their chosen ones.

Zen-Aku also revealed that his power came from the phases of the moon, as he was at his strongest when it was full. During the New Moon's phase, he was revealed to be human when Cole saw a young man in the river, accompanied by the wolf cub Zen-Aku had rescued.

Zen-Aku was able to control his own Wild Zords, which he called the "Dark Wild Zords", using his flute plate to summon them. He could also combine them to form the Predazord. Zen-Aku's primary weapon was his Crescent Blade, whose blade could open at two notches. While in that position, his weapon's attack was the "Crescent Wave", which was a blade of dark energy that could disable almost any of his opponents.

Meeting Animus
Over time, Zen-Aku's true nature had been revealed, as he began slowly acting more and more human, by starting out with caring for Alyssa, the White Wild Force Ranger and rescuing a wolf cub from an attack from another Org. The Rangers began to grow confused, and even more so, when the spirit of Animus appeared in the sky and urged Zen-Aku to simply "Remember." However, just as his human self (Merrick) was about to break free of Zen-Aku's curse, Nayzor arrived and turned him into his willing slave, making him unable to be reasoned with.

The Ancient Warrior
When Princess Shayla learned that Zen-Aku was really her faithful Guardian Merrick, she tried to piece together the events of the final battle in Animaria. She discovered that the source of the curse put on Merrick was not the Wolf Mask, but his Predazord. After Master Org was defeated, Predazord had turned evil, and its chosen Guardian along with it. She informed the Rangers that defeating Predazord was the only way to break Merrick's "curse". With a new Wild Force Megazord combination, they did so and reverted Merrick to his human form, destroying Zen-Aku's mask in the process.

Unfinished Business
Merrick thought Zen-Aku was gone forever when his Predazord was purified of the evil that poisoned it, but, a few episodes later, Zen-Aku returned with an agenda: to remerge with Merrick and become complete once again. With the return of the Wolf Duke Org, the Rangers began to question Princess Shayla about this event. Princess Shayla explained that when Zen-Aku's spirit merged with Merrick, it was divided among the Mask of Zen-Aku, Merrick, and his Predazord, but with Predazord and Merrick now good again, Zen-Aku (who was now free because the purification of the Predazord broke both curses on the mask, including the one that imprisoned his Org spirit) possessed all the evil power that was once divided, and was now much stronger than he had previously been, proving it by holding his own against the Predazord and the Wild Force Megazord Striker while even being able to block the latter's finishing move. However, after Merrick used a new trick pool shot (taught to him by Willie at the Road House) involving the Predazord's Gator Staff and the Armadillo Zord to break Zen-Aku's horn and weaken him, the Wolf Duke Org was apparently destroyed by Predazord's "Revolver Phantom" attack.

Final Appearance
After Master Org was defeated, Merrick traveled the world, and Zen-Aku returned, offering to join him, since they were both "lone wolves looking for redemption".

Powers and abilities
Unlike other Orgs, Zen-Aku has enhanced strength, stamina, resistance, agility and speed that exceeds that of the Wild Force Rangers. His primary attack is the "Crescent Wave",the only special attack of his blade, which was a blade of dark energy that could disable almost any of his opponents. Though he is a formidable opponent, his greatest strength comes out during full moons. Strangely, Zen-Aku also had his own set of "Dark Wild Zords" and can also capture other Wild Zords for his own uses.

Crescent Blade
Zen-Aku's primary weapon which was a large double sided blade. Zen-Aku's primary attack with the weapon was the "Crescent Wave".

Flute knife
He can also use this weapon to quicky strike an opponent, but it is primarily used to summon his Dark Wild Zords.

Dark Wild Zords (Former)
Zen-Aku was able to control his own Wild Zords, which he called the "Dark Wild Zords", using his flute knife to summon them.
 * Alligator: the alligator was the whole body of the Predazord
 * Wolf: it was the left arm of the Predazord 
 * Hammerhead Shark: it was the right arm of the Predazord

He was able to combine them to form the Predazord.

Stolen Wild Zords
Zen-Aku could also freeze Animal Crystals and take them under his possession. He stole the Black Bear, Polar Bear, Giraffe, and Elephant Wild Zords. Like the Wild Force Megazord, his Dark Predazord could use the stolen Wildzords as arm attachments in battle.

Weaknesses
He also has several weaknesses like:

New Moon
As if it were a real werewolf, he loses all his power during the new moon and return to his human form, Merrick Baliton. However since they are independent entities now, is possible that he doesn't have this weakness anymore.

His Horn
Like all the Duke Orgs, whenever he loses his horn, he loses his power and his life.

Sacred water
Like all the Orgs, he suffers when touching the Sacred water of the temple (though he can survive to this if he cut his horn, but he'll die eventually).

Trivia

 * Zen-Aku name might mean "Meditative Evil" because "zen" in Japanese originates from "Zen Buddhism" while "aku" means "Evil". It might also mean "Total Evil", as "zen" is one possible reading for "all".
 * He may or may not have night vision, since his eyes are always glowing and he fights at night with ease.