He is the only child of the Samurai Lord. As he became a young child, he witnessed his kingdom ravaged by Aku and spent the rest of his youth getting trained by many people across the globe. As he became twenty-five, he returned to Japan and realized that Aku enslaved his people and abused his father. His father gave him the sword that banished Aku so he can finish the demon off. He found Aku's hideout and was very close to defeating Aku. However, Aku sent the Samurai into the far future, where Aku is the ruler of a dystopia filled with aliens, robots and bounty hunters that are all after the Samurai. He met three men who referred to him as "Jack", an alien slang that means "friend". He took that as his name and helped a village of dog-like people defend themselves from Aku's Beetle Drones. Jack set himself on a quest to find a time portal and finish what he started. In his many attempts, he failed and eventually lost his sword.
Fifty years have passed since Jack lost his sword and gained a beard with no age whatsoever, which is a side-effect of his arrival to the future. He has lost all hope into getting back to the past. One day, he encountered a comical robot musician named Scaramouche, who works for Aku. Scaramouche noticed that Jack lost his sword and attempted to call Aku before the battle began. After Jack won his battle against the robot, he was targeted by the Daughters of Aku, a group of seven sisters bred by Aku and his High Priestess to assassinate Samurai Jack. In a vicious battle, he killed all except one. The sole survivor, Ashi eventually trusted and fell in love with Jack. Jack was visited by a spirit known as the Omen who believed that Jack must commit seppuku because of his quest being failed. Ashi intervened and helped Jack get another chance in life and find his sword. Jack realized that his negative emotions is what made him lose his sword. In a mental ritual, he was given back his sword by the gods for being worthy. Ashi killed off her mother as Jack is calmly distracted by his peaceful state. Jack and Ashi found a destroyed time portal, which turns out to be the portal owned by the deceased Guardian, whom Aku killed. Aku and Scaramouche arrived, believing that Jack lost his sword. Once Aku saw the sword, he destroyed Scaramouche. Aku revealed to Jack that Ashi and her six sisters are literal daughters of Aku, which surprised him. He was imprisoned by Aku, which gave him the idea to convince Ashi to help him go to the past with the help of his friends over the years.
Jack finally returned to the past with Ashi and killed Aku with a final blow. As he was about to get married with Ashi, she died because of Aku's death. While it made Jack sad, he realized that he prevented a grim future.
*Samurai Jack is voiced by Phil LaMarr, who is also known for voicing Static Shock, Hermes Conrad from Futurama and Hector Con Carne.