The Shinobi (also known as Warrior of the Night or simply The Ninja) is a minor antagonist in Samurai Jack. He is a silent robotic ninja who specializes in striking from the shadows, and was one of the many subordinates that Aku sent to kill Jack.
Shinobi was a humanoid robot about Jack's height, wearing a black ninja outfit called a Shinobi Shizoku that covered his entire body, save for a dark red visor with glowing red eyes. Wielding a pitch-black katana, he was a master of stealth and assassination and practiced against Samurai Jack droids to perfect his art.
Shinobi first appeared in what seemed to be some sort of temple where Jack was praying. After swiftly and silently infiltrating the temple, he approached the Samurai and quickly cut him down before the latter could reach for his blade. However, this was revealed to be a simulation in order for Aku to test the bounty hunter's skills. Satisfied, the Master of Darkness sent Shinobi to kill Jack.
The robotic ninja is later seen stalking Jack in a jungle, but before he could attack, a small boy ran out of some bushes while a robotic lobster-like creature was chasing him. Deciding to bide his time, Shinobi hid in the shadows and continued to follow Jack as the latter defeated the robot and accompanied the boy to his village. He continued to observe Jack from the sidelines as the samurai destroyed the horde of robotic lobsters attacking the village. When the boy lingered behind to watch Jack's fight, Shinobi kidnapped him and fled to an abandoned tower near the beach.
Taking the bait, Jack soon arrived at the tower to find the boy hanging from the ceiling. Shinobi attacked while the samurai was distracted, but Jack narrowly evaded the strike and freed the boy from his bonds. With the "bait" fleeing the tower, Shinobi fought Jack for a while, using the shadows to strike from unexpected angles. Realizing the ninja's strategies, Jack decided to fight in kind, using the light instead of the darkness to hide. With the playing field leveled, the two warriors clashed fiercely, but the setting sun slowly depleted the tower's light, tipping the fight in Shinobi's favor.
When the light in the tower was all but gone, Shinobi moved in for the kill, which proved to be his undoing. Seeing the beam in front of him vibrating from the ninja landing on it, Jack used his sword to reflect the last sliver of light into Shinobi's eyes. Blinded by the light, the robotic assassin dropped his guard for a fatal instant, allowing Jack to throw his sword and impale him to a post. As the light faded from Shinobi's electronic eyes, he slid down the post, being cut in half by the sword still impaled in his body.
Shinobi was presumably erased from existence after Aku's destruction in the past, since he was created to slay Jack.
- Master Infiltrator: Shinobi could infiltrate any area or building without being detected, even by Jack.
- Martial Arts Master: Though he specialized in assassination, Shinobi was highly proficient in hand-to-hand combat, utilizing punches and kicks in conjunction with his sword to catch his opponents off-guard.
- Master Swordsman: Shinobi was extremely skilled with his sword, matching (possibly slightly exceeding) Jack in open combat.
- Darkness Camouflage: Shinobi's signature ability allows him to become completely invisible as long as he is in darkness; even a simple shadow is enough to make him impossible to detect. However, his presence can still be detected by his interaction with the environment, such as footprints left on the ground or vibrations from his landing on an object.
Shinobi's Ninjato: Shinobi wields a black sword as his main weapon and assassination tool.