I like his little smile Gaja not having a good day The face of a Kaasu

Gowdomu's Heart, HL 80 Gowdomu's Brain, HL 130 In the series we first encounter the ancient Shinto priest Gaja, whose faceless minions are the Kaasu and who seeks to power Gowdomu. The word used to describe him is 大神官 Daishinkan. It's been 40,000 years since he's seen action, yet he speaks the same Japanese as our heroes. Gowdomu was buried beneath the sea, its Heart hidden inside. Gaja was sealed into a crypt where he existed as stone and, when awakened, out of the walls emerged also his minions, the Kaasu. After the Boukenger defeated him and secured the Gowdomu's Heart, he was taken prisoner by Ryuoon. Ryuoon intended Gaja to lead him to the Gowdomu's Brain. Unfortunately for both of them, the fact that Ryuoon is an evil, bullying arse was key in allowing the Boukenger to also retrieve the Brain. Gaja had the unfortunate experience of being the most easily beaten but he never gave up. He seemed to be the only one trying to forge some sort of alliance to defeat the Boukenger. He kept giving the others a handful of Kaasu to use. He has a photographic memory and a definite technological bent, as he kept building Gowdomu Engines to power mecha... and to power himself. For, while the other groups got all the attention, Gaja embedded three Gowdomu engines in his chest. He went on his own mission, to absorb the evil power from Pandora's Box, and attack the Precious Bank where, despite the fact that Dr. Makino had the whole building self-destruct, Gaja was able to collect the Gowdom Heart and absorb it. Gaja then put himself into a coccoon while he mutated into a more powerful form. Much to his dismay, the Boukenger defeated him and he lost his additional power. However, he survived and put himself back in stasis for another era.

First battle with the Gowdomu. Gowdamu engines, unite!

Ryuuoon They said I was mad.  Let them laugh, now! in shock and defeat?  Never!

JaryuJaryu LizardsThe second enemies we encounter are the reptillian Jaryuu. Their leader is Ryuoon, who sees nothing odd about kidnapping and brutalizing another enemy of the Boukenger into doing his bidding. This is a weak point of his, I'm afraid. He created his servants, the Jaryu. He also certainly created 大邪竜ドルド DaiJaRyu Dorudo, the giant cyborg creature that snaps up Gaja at the end of Task.1 and he destroys trying to kill the Boukenger in Task.2. Nothing seems to kill him, though he can be brought down for a short time by severe injury. This is because he was once human, a treasure hunter who turned himself into a monster. Betrayed and left for dead by the men he'd travelled with, he burns with hatred of all humans and does not in the least want to be human. The Jaryuu are all clones, so he is rather indifferent to their deaths. So, though, are they. They are not very bright. One of the interesting things about the Jaryu is that they can bud off vicious lizards who make excellent spies but, to the Boukenger at least, are pretty useless in a fight. As the second enemies on the scene, they were the third to be destroyed as the writers thought the reverse order was neat. Ryuoon found he'd overrun the ability of his Helmet, a Precious itself, to regenerate him. In a desperate measure, he pretended to die but was hiding out as glop inside his helmet. The Boukenger sent the helmet off to the Precious Bank, then Akashi had to defend it when Ryuoon regenerated inside. But Ryuoon lost his reptillian characteristics and died a human. Presumably he did, I mean Satoru made it so why not Ryuoon? We see at the end that there are still some Jaryu about. Survivors, or is their creator alive after all?
Makes the monsters big.

Yami no Yaiba Maboroshi no Gekkou Kaze no Shizuka

Third we encountered the Dark Shadow. 幻のゲッコウ Maboroshi no Gekkou, who is a mystical blue owl, creates their monsters and directs his two minions. He was once human, but went up against a powerful monster/Precious which, well the whole adventure turned him into an owl but he bound the wild power and kept it in check for long, long decades. When you look at the monsters they created, it seems suspiciously like a joke. "Something old, something new, something borrowed, something blue." Dark Shadow's monsters tended to be a blend of something old and new, you could say the power that created them was borrowed, and blue was definitely their preferred color theme.
Yami no Yaiba, a strange being but he was one of the most powerful evil ninja there is. He'd also been around quite a while. Years ago he slaughtered a group of treasure hunters but left the child among them, Masumi, alive to see what he would become. He turned against Maboroshi no Gekkou to pursue evil in his own way. Namely, by releasing the wild power his leader had bound so long ago. He betrayed the others and attacked Shizuka but left her alive. He used Masumi to call down the Darkness. He was the second of their enemies to be destroyed.
Kaze no Shizuka, a lovely young woman who has the spoiled, bratty personality of a six-year old, which offends me. She arrived showing such promise, but they barely let five minutes going by without demonstrating her usual personality. I really hate it when characters are childish. BoukenBlue usually seems to find her hilarious, which drives her around the bend. And I think she's only getting worse.

The Dark Shadow as a group (consisting really of two people) was never destroyed, the writers deciding they were harmless.

Kaze no Shizuka at play

This is Gaiand this is Rei

Fourth, much to his dismay Gaja was instrumental in creating the Quester. The Quester originally were two powerful Ashu. One, Gai, is responsible for killing Eiji's father. Gai and Rei were killed fighting the Boukenger. Gaja resurrected them intending to make them into useful tools, but they were beyond his control. Indeed, beyond anyone's. They took from the other three evil sets whatever they wanted, but as the last enemies to come on the scene, were also the first to be destroyed.

Gai, having fun.HyougaReiOoga

Ashu are a predatory species, sadistic and energetic at the least. Mr. Voice indicated they are an offshoot of the same evolutionary tree as we are. Pity they got all the power. Gai mostly seems just to be raw power, he fights with happy enthusiasm, makes bad jokes and delights in chaos. Hyouga seemed to be along for the ride with him, a loyal friend and follower. Rei is tremendously powerful, thirsts for human blood, and is able to expose the secrets of the heart. Most of the Ashu have been sealed off in a Precious, the Hyakki Kagami (Mirror of a Hundred Demons). According to the Boukenger book, there are 数百万 A.K.A. millions of Ashu in there. We know of at least four who weren't. Eiji's mother, Gai, Hyouga and Ooga (Ogre?). Ooga was, by the way, in love with Kei and he did not take losing her to Eiji's father well at all.