Raizen(Yu Yu Hakusho Profile)
Raizen is Yusuke's ancestral father and is one of the three rulers of the Demon World. He's played a relatively short role in the series but has a very interesting past. He reveals to his son the long story of his life which contained both miserable and wonderful events just before his demise.
Raizen has messy, long, and light-brown hair. He has a tattoo on the middle portion of his left cheek and a green headband wrapped around his forehead. He has a fairly muscular but nearly lifeless-looking body, due to having not eaten anything for nearly a thousand years. However, his seemingly ordinary and delicate appearance is actually in sharp contrast to his awesome power. He holds the power to defeat any S-Class demon, even the other two Makai Rulers, without getting up from his throne.
Despite his brutal reputation as a warrior and a savage beast who feeds on humans, Raizen has a very loving and caring personality and though he may not seem like it, he is a man and a word of honor, keeping his words even when someone he's made a promise to is no longer there to see it. He's chosen to keep his promise of not eating a human to the only woman he's ever loved over eating, staying strong, and thereby remaining in greater power and control of the Demon World forever. Yusuke did not realize how proud he was of his father until he's heard the words of Raizen's comrades saying how honorable he was. Even in death, Raizen is always there to give the best advice that he can give Yusuke and guide his son to the right direction.
Raizen is at least two milleniums in age. Like all blood-thirsty demons, Raizen made a living as a nomad, moving from place to place in search for humans to eat. During his younger days, Raizen would constantly raid villages and slaughter countless people for food. However, unknown to him, his outlook about humans serving demons as food would one day change. After meeting a very beautiful human woman(Yusuke's ancestral mother) and falling in love with her, the mighty demon king vowed to her never to eat humans again. The day that Raizen left her was also the last time he'd see her, as she supposedly died after giving birth to a child. Raizen waited for generations in hope for her to come back as a reincarnated being but she never has.
More than 700 years later, realizing that he'd soon be passing, Raizen ordered his three most loyal servants to pay a visit to the Living World to retrieve his descendant who would be the rightful heir to the throne. About a year after Yusuke arrived in the Demon World, Raizen passed away, and it's now up to his son to continue what he's left behind.
Toushin Raizen is the Master of War. He's battled the other two kings just for the sake of fighting for several hundred years without having any slight difficulty. He is possibly the strongest character in the series. Raizen's old comrades, particularly Enki, are witnesses of his phenomenal power. Even by S-Class level standards, Raizen's physical strength is incredibly high. Even Yomi admits that Raizen's always been the very one he ever wanted to defeat and so he tried, but to no avail as Raizen was in a totally different league of his own. Upon sensing that his son was on a tight leash during the battle with Sensui, Raizen took over Yusuke's body and eliminated Sensui in a flash, even Sensui's Sacred Energy was completely helpless. During his first meeting with Yusuke, he easily knocked him several feet away by just releasing a small amount of energy through his hand after spreading his fingers, despite the fact that Yusuke already had a level of power comparable to an S-Class demon's, and he beats up Yusuke for a brief while to make him realize that his power was pathetic and nowhere near the other two kings', without moving from his seat. Many of Raizen's comrades have stated that most of them have tried to defeat him in the past but never succeeded for Raizen was simply the strongest demon that had ever lived. It is believed that it would take Yusuke's already impressive power another 300 years just to even come close to his father's.