This was requested of me, I didn't know what exactly they wanted so I did this...
Zen-Aku basically means good (Zen) and bad (Bad). Both were tormented warriors who once were good, they put on a wolf mask that took them over and were bad to the Rangers. They stole their Power Animals and had their own. They then had some redemption and redeemed when the curse was broken. Unlike Loki who was destroyed forever, Zen-Aku lived and then roamed the Earth alongside the Lunar Wolf Ranger.
3000 years ago, Merrick donned a wolf mask, transforming him into the evil Zen-Aku. Zen-Aku battled the original Wild Force, and was defeated and imprisoned. He awakened in present day, and sought revenge on the successors of the Wild Force powers. Zen-Aku's memory was cloudy - he did not remember his true identity, and did not clearly recall the events which led up to his imprisonment, thus making his motives unclear at times. He was eventually broken free of the spell, and was reverted to Merrick, who then became the Lunar Wolf Ranger. The mask of Zen-Aku eventualy reformed, and Zen-Aku was brought back to life, no longer needing a host to live in this world. He went after Merrick to try and merge with him and regain the power they had as one. Merrick was victorious, and destroyed Zen-Aku again. After the final battle against Master Org was over, Merrick left to travel the world. Surprisingly, he was approached by Zen-Aku, who had once again come back to life. This time however, he was not out to do evil. He sought redemption for his evil deeds, just like Merrick, and joined him on his journeys across the globe.
An Org whose evil energy was contained inside the Dark Wolf Mask. He transformed Shirogane into an Org and corrupted his three Power Animals. He wields the Crescent Moon Blade which can perform the Crescent Wave and Moonlight Sonic attacks, and like Tsuetsue, he had his own seeds that could enlarge Orgs called Wolf Seeds. Loki battled the Gao Warriors, and was defeated and imprisoned. He was awakened in present day by Ura, and sought revenge on the Gaoranger, successors of the Gao Warriors to satisfy his one thousand year grudge. Loki's memory was cloudy, he didn't remember his true identity, and couldn't clearly recall the events which led up to his imprisonment, thus making his motives unclear at times. To prevent him from remembering the past, Ura implanted a bug into Loki's head which would further cloud his memory, and strengthen his resolve in destroying the Gaorangers.
The Gaorangers discovered that Loki was truly Shirogane and they set out to revive him. GaoGod even created an eclipse to cut off Loki's power source, and allow the Gaorangers to reach through to Shirogane for a brief period. To break the spell over Shirogane, Gao Hunter needed to be defeated in battle. With GaoKing Striker, they were able to take down the Gao Hunter, scattering its Gao Jewels. Amidst the chaos lay Shirogane, restored back to normal, with a broken wolf mask nearby. The 'Evil of A Thousand Years' mask eventually reformed, and Loki was brought back to life, no longer needing a host to live in this world. Loki attempted to kill Soutarou for using him and his power. Loki was eventually defeated when GaoSilver joined forces with the other Gaorangers and Loki was finally killed by GaoHunter Justice. But the evil energy escaped and Ura began to cultivate it. Shirogane briefly became Loki again when Ura forced him to reabsorb the stronger evil energy, but he was able to reject the power, unaware that it was all part of Ura's plan.
JAKQ Strengthening Capsules
Goggle Brace 
Dynabrace 
Techno Brace 
Change Brace 
Prism Flash 
Masking Brace 
Twin Brace 
Turbo Brace 
V-Changer
Cross Changer
Dino Buckler / Power Morpher 
Aura Changer
Doron Changer 
Power Brace / Zeonizer
Accel Changer / Turbo Morpher
Digitizer / Astro Morpher
Ginga Brace / Transmorpher
Go Brace / Rescue Morpher
Chrono Changer / Chrono Morpher
G-Phone / Growl Phone
Hurricane Gyro / Wind Morpher
Dino Brace / Dino Morpher
SP-License / Delta Morpher
MagiPhone / Mystic Morpher
Accellular / Overdrive Tracker
Geki Changer 
Solar Morpher
Go-Phone / Cell Shift Morpher
Shodo Phone
