Izumo

, also known as Gyu-oh (in his demon form) was a half-human, half-demon born to a human man named Izumo and an unnamed female bull demon.

History
While traveling the lands in order to find a way to become a full-fledged human, Izumo learned of the Shikon no Tama, a jewel that purportedly had the ability to grant any wish made by its bearer. To his dismay, he discovered that the Jewel was shattered into many shards and that it would take a lifetime to reassemble. However, by forming an alliance with Orochidayū, a demon who also desired the Shikon's power and commanded hordes of lesser demons, Izumo devised a method to recreate the jewel again and again by harvesting the souls of numerous, random villagers. Though not nearly as powerful as the one made by Midoriko, the mass-produced Shikon Jewels could still empower demons considerably for a short period of time, but due to impurities, the imitations proved toxic to humans. Through more research, Izumo discovered that he could create a true Shikon Jewel by using the souls of those who possessed greater than normal amounts of courage, knowledge, love and friendship, which he found in Inuyasha, Miroku, Sango and Shippō respectively. He captured Kagome, planning to use her spiritual powers and three jewel shards to create the new Jewel.

In his final moments, Gyu-oh, desperate to create the new jewel before dawn (at which point he would become human again and therefore easily defeatable), swallowed a number of imitation Jewels to overcome Inuyasha. He was unable to defeat Inuyasha before daybreak, and when the sun rose, he reverted again to Izumo. With his human form unable to withstand the jaki of the fake jewels, he died, poisoned by his own creations. His lower half was unable to finish the transformation, leaving him a freakish satyr; his final words expressing regret that he was unable "to die as a human".

Physical description
Gyu-oh was unique among half-demons. Instead of maintaining a half-human, half-demon appearance all the time as all other half-demons in the series are shown to do, he was fully human during the day and fully demonic at night. It was probably this trait that drove him into madness and fueled his desperation for the Shikon Jewel (and also explains his "unusual" obsession with the sun). While in human form, Izumo was pure--more so than normal humans to the extent that wild birds would land and rest on him.

Powers & Abilities
As a bull demon, Gyu-oh was quite formidable, capable of intimidating other full demons into doing his bidding and proved to be a worthy opponent to Inuyasha (albeit with the help of multiple faux Shikon Jewels). He possessed immense size and strength and his breath was a potent shōki.

Weapons
Gyu-oh possessed a club that had multiple fake Shikon Jewels embedded within it, making it extremely powerful. The club was so powerful that Gyu-oh was able to completely destroy the ground surrounding Inuyasha and the other's feet, sending them falling.

Trivia

 * Despite the common discrimination against half-demons, Orochidayū seemed to genuinely like Izumo/Gyu-oh and treated him with respect rather than grudging tolerance. Whether this was due to their mutually beneficial arrangement or because he was impressed by the other's cunning is up to speculation.
 * Izumo/Gyu-oh is the archetypal Dr. Jekyll and Mr. Hyde.