Hattori Tatsuo was born into an extremely powerful aristocratic family in feudal Japan. As a child, he suffered violently from smallpox to one eye. He pulled out the diseased organ personally. Unfortunately, because of his deformed appearance as a result of doing so, his mother saw him as unfit to continue the aristocracy of his family. She began to spoil and favor his younger brother, and resented Hattori intensely. She even tried to poison him, but he survived due to his high tolerance to poison. As a result of his survival, he became psychologically insane but his most famous result of the survival was that his eye became intensely green, like Jade.
Hattori murdered his younger brother to ensure his rise to power, and served under his father in his first battle at the age of sixteen. His father was killed in battle, presumably by Hattori himself for the same reason as his brother's death. He later turned on his mother, avenging himself on her by pulling out both of her eyes. After having dealt with all three of his family members, Hattori took over the Tatsuo family and waged a long and brutal war on Japan, intending to become Shogun.
Rise and fall from power
He allied himself with Daimyo Kamakura, and the two of htem came dangerously close to ruling Japan. However, Kamakura betrayed him to side with Daimyo Takatomi - the leader of Hattori's opposition in the war. During one single, bloody battle that spanned several days and nights, Tatsuo saw his son cut down in front of him by Takatomi's greatest warrior, Masamoto Takeshi. This single act would inspire Tatsuo into violence against Masamoto for the rest of his life.
Tatsuo himself was captured at the end of the battle, but Tatsuo outwitted his captors. He replaced himself with another man who looked exactly like him - except, obviously, for having two eyes, but Tatsuo soon remedied that. This man was executed in Tatsuo's place, and Tatsuo sought out to avenge himself upon Masamoto.
Becoming a Ninja
Tatsuo, now adopting the name Dragon Eye, first sought out a master swordsmith named Kunitome, ordering him to make the finest sword possible. The sword, upon its completion, was christened Black Cloud - on accounht of the fact that, on the night that it was completed, the local village was demolished by a violent thunderstorm. After being presented with the sword, Dragon Eye tested it on six prisoners and later Kunitome himself, to prevent him from making a finer sword.
Later on, Dragon Eye joined a Ninja clan in the Japanese mountains, manipulating the Grandmaster Soke into teaching him everything about the Way of the Ninja. Dragon Eye frequently, throughout his training, showed sadistic and violent tendencies that made Soke question his loyalty to the clan, but every time these suspicions arose, Dragon Eye would show positive signs of becoming a Ninja that erased all suspicion. Soke eventually taught Dragon Eye the art of Dim Mak (Death Touch - the art of causing pain to an opponent by targetting pressure points).
Later on, Dragon Eye left the clan and started his own clan.
Revenge, and Jack Fletcher
With the required skills and experience obtained, Dragon Eye started his vendetta against Masamoto. He started by murdering Masamoto's eldest son, Tenno, ironically spurring Masamoto into a vendetta against Dragon Eye. He was later on hired by Daimyo Kamakura and the heretic priest Father Diego Bobadilla to help both of them wage war on Japan. Daimyo Kamakura promised the Ninja to redeem himself for the betrayal during the war by giving Dragon Eye a rise back to power.
Dragon Eye's first mission was to steal a rutter (A traveller's logbook that secretly contained information that would make the owner master of the European seas). Dragon Eye was made unaware of the rutter's true importance, naturally. He and his clan ambushed the ship Alexandria (Captained by John Fletcher), and murdered John Fletcher right in front of his son, Jack. Before he could steal the rutter, Masamoto and his men appeared and fought them off.
Throughout the next two years, Dragon Eye made several attempts at stealing the rutter, eventually succeeding after sacrificing one of his own lieutenants in the process. After this, the Second Japanese war began.
War and defeat
For the duration of the war, Dragon Eye pretended to be in the employ of Father Diego Bobadilla, who would keep hold of the rutter until it was deciphered (The logbook turned out to be encoded). When the pupils and teachers of Masamoto's school resided at the castle where Diego Bobadilla resided. Jack Fletcher exposed Father Bobadilla as a traitor, but not before Dragon Eye arrived, having deciphered the rutter.
He killed Father Bobadilla, having no further use for him, but Jack Fletcher tried to escape and the Ninja pursued him. Dragon Eye revealed that this entire war was, in Dragon Eye's perspective, a revenge upon Masamoto for killing his son. After Jack refused to hand over the rutter, Dragon Eye attacked him.
A climactic duel broke out, spanning the full width of the castle - which had fallen under attack from Kamakura's troops and was in the process of being destroyed. The duel led to the rooftops of the castle, where Akiko and Yamato (Masamoto's niece and youngest son), joined in and tried to defeat the Ninja. The Ninja defeated Jack and Akiko, but Yamato attacked the Ninja again, intending to avenge his older brother's death.
The struggle took Yamato and Dragon Eye over the edge of the castle, where Yamato allowed himself to fall, taking the Ninja with him.