The main villain group was the "Evolian", which are initially amoeba-like entities, that came from the meteorite which fell on Earth 65 million years ago. However, the Evolian also included renegade Ryujin. Moreover, midseries, an evil ranger, Abarekiller, appeared and became a very dangerous adversary against the heroes.
I'll separate the "villain" section in three parts
The main villains are the Evolian
1-1) Evolian: the amoeba-like creatures
The Big Bad of the series, he's the Evolian God, a parasitic like entity which doesn't have a definite appearance, and lives through diverse hosts. When the meteorite fell on Earth, he was split in two parts, one part in Dino Earth, the other in Another Earth. The Dino Earth part was the leader behind the Evolian invasion, and at the beginning of the series, had the "Tree of Life" as its host. However, when two Ryujin warriors were captured, including Mahoro, a pregnant woman, he forcibly entered a part of him into Mahoro's body her unborn child. Once born, that child became a mobile host for Dezumozorya, and his vessel to give orders and punish his subordinates Dezumozorya's aim is to assimilate all life in himself, and he doesn't hesitate to cruelly punish his followers when they fail, and, generally speaking he doesn't care for anyone, but himself, and will sacrifice even his most devoted servants if necessary. However, being split in two had weakened a lot Dezumozorya, and he had often to stay in a dormant state. It has been revealed late in the series that the "Another Earth" part of Dezumozorya was inside Mikoto Nakadai. Once Dezumozorya came in contact with his second half, he became more powerful, and did everything to become one again. His main weakness are "Dino Guts" who weakens him a lot and are able to destroy his "evil life" essence. During the last episodes of the series, he used very different hosts, that he has no hesitation to discard when they were not useful anymore (first Lijewel, then fusing with Mikela and Voffa), to try to destroy the heroes, but, eventually, after several battles, the last one during which he used the Evolian base at his body and tried to destroy life on Another Earth by preventing the sunlight to reach it with hundreds of Anomalicaris ships, he's been completely destroyed by the heroes and the Bakuryuu when they sent all their Dinoguts to defeat him. As an ultimate act of cruelty, he tried to take in death with him the heroes and the Bakuryu, but fortunately, thanks to Yukito's plan, he failed again for the last time.
b) The Messengers, and Monster makers (with brief descriptions of the Monsters of the week)
He's obsessed with making masterpieces Trinoids, even if his aesthetics tastes are pretty controversial, even among his fellow Evolians (notably Voffa). He has a friendly rivalry with Voffa, and boasts at being more efficient than him in creating monsters. In episode 24, he's shown a curious side, and he seems interested in discovering stuff about Another Earth and its creatures and technology. He's also shown an affable side of his personality, which is shown in his interaction with Rije and in episode 24, with the high school girls. At the end of the series, he was forced to fuse with Voffa to become Dezumozorya's host, as Dezumovora, and fought the Abaranger in that form. However, at the end, Dezumovora was defeated by Abarekiller and Killeroh, with Dezumozorya leaving him and Voffa to die.
Voffa only wants to compose the best music ; as such, it takes a lot of time and effort for him to create Giganoids. Like Mikela, he's shown a curious, and even affable side that is shown in his interactions with Rije and when he visited Another Earth. At the end of the series, he was forced to fuse with Mikela to become Dezumozorya's host, Dezumovora, and suffered the same fate as his comrade, when he was Dezumovora was defeated by Abarekiller and KillerOh, and he was left to die as Dezumozorya fled back to Dino Earth.
The Evolian's headquarters.