Ryuon the Dark Adventurer

Ryuon of Boukenger served as one of the darkest and most bloodthirsty characters in history. He had a dark secret which wasn't known but all viewers can see is his desire to get and control whatever "Precious" he can for him to reanimate the world as he saw fit.

He first appeared in the second episode of Boukenger and fell into an uneasy alliance with the final nemesis Gaja (in case you forgot, Boukenger has more than one faction involved) or even with the Questers at times. He and Satoru/Bouken Red developed a conflicting side for each other as opposites as adventurers. He pursued power which Satoru/Bouken Red didn't. He was one who believed in strength ruled all as he let his own genetic monstrosities fight each other and the survivor become the chosen Great Evil Dragon. On the first encounter, Bouken Red left a scar on him which he considered was a curse.

He revealed his own selfish motives when he decided to use Raja to find the Aqua Crystal which I believe he would try to drown the rest of the world which again caused another serious battle with him and Bouken Red.

Sooner while the Boukengers were in search for the Sword of Lemuria (who was also Zubaan), his origins were soon revealed by Professor Igarishi who originally hated Search Guard Successor that he was alive for 200 years and was once a man. He was left alone in his expedition for the Lemurian artifacts and because of this, he grew bitter, experimented on himself and became a "dragon" which he had the Lemurian helmet which could prolong his life but for how long is uncertain. He was defeated by Bouken Red when he couldn't get the Sword of Lemuria because of his impurities and he lost the Egg of Lemurai to Gaja.

He had an uneasy alliance with the Questers during the time the Sun of Lemuria revealed Natsuki/Bouken Yellow's origins. Eventually he was betrayed when the Questers used the Homolculus for their own. It was later revealed he was running out of power and he wanted to be reenergized. Unable to accept his fate, he decided to feign death and recharge in the Helmet of Lemuria which he used to prolong his life to get more Precious to empower himself which resulted in the rather cool final battle between him and Satoru/Bouken Red which soon broke the powers he had.

He was going to try and get the Egg of Lemuria and went to the timed to destroy SGS Museum. Satoru/Bouken Red offered him help which he refused. As Satoru/Bouken Red was able to escape with the help of Zubaan, it is most likely he perished but a few of his Evil Dragons still exist (probably due to a laboratory accident) suggesting he may still be alive but without his powers to serve him anymore.