Dr. Los originally created the Blue Knight as a handsome young robot adult named Blue Bon who is capable of shape changing. Later he built a younger sister, Maria, and small brother, Tonto, for him. He loved them all just like his own children. Maria later became the bride of Count Burg after he was taken by her beauty despite being a robot. But the Count showed his true colors towards robots when he began to abuse Maria. After Tonto found out he took a flying car to rescue his sister but they were caught and the cruel Count smashed both Tonto and Maria to pieces and dumped them on Dr. Los’s doorstep. Blue Bon went insane with grief and rage. Because Los couldn’t bear the thought of just throwing their bodies away he modified Blue Bon with the ability to transform sometimes into Tonto and other times into Maria. But he did this without Blue Bon’s knowledge and when he found out he began to hate even his own creator. Blue Bon felt like a freak and so Dr. Los built him a suit of armor and a helmet to conceal himself. Then he left to pursue his dream of destroying the robot law and building a nation where robots can be free.
1960 TV seriesThe Blue Knight only appears in a two-part episode titled "Blue Horseman" Part 1+2 (episode number:179 and 180). The Blue Knight captures Count Burg to avenge his brother and sister. When Dr. Los appears before him to explain the truth about his past, the Blue Knight becomes enraged and throws a spear to kill him. However, Astro intercepts it to save Dr. Los and is destroyed instead. Professor Ochanomizu rebuilds the Blue Knight and tells him while he may hate humans some robots are prepared to lay down their lives for them. Just like Astro died to protect Dr. Los. The Blue Knight is humbled and consents to allow his creator to tell Ochanomizu his history. He then takes off his helmet and deeply apologizes for what he did to Astro and hopes that Ochanomizu and Los will repair him. Count Burg seizes his chance and breaks free from his guards. Snatching up his own spear he drives it through his back while he is unprotected by his armor making him explode.
The Volume of the Blue Knight filmThe Blue Knight never appeared in the 1980's TV series. A short film called Volume of the Blue Knight was released instead. In this film, he is referred as the 'Blue Bon' while his creator is known as 'Doctor Ross'.
Astro Boy tries to convince him to change his mind about the humans. But he misunderstands, assuming that he is an enemy for siding with them. While fighting, General Lamp, and his airborne subordinates join the battle, as Lamp hates robots. Blue Bon attempts to attack them, but Astro stops him. Astro Boy's interference gives the General and his subordinates a chance to strike and the two crash into a building. Uran, Doctor Ochanomizu, and Doctor Ross quickly meet them on the building. Ross speaks of Maria and Tonto to him, he replies mentioning their sad past and the cruelty humans have shown robots in general. Later on, the building starts to collapse and Astro tries to save everyone inside. Blue Bon, having remembered more about his family, has a change of heart and takes Astro’s place to hold up the building. Just as Astro gets the others to safety, a huge explosion goes off. Blue Bon is found lying in the rubble, he and Astro have one last conversation before he closes his eyes, he had finally changed his view of humans. Doctor Ochanomizu and Astro Boy watch the sunset in the distant sky, still believing an understanding between humans and robots will come someday.
2003 TV seriesThe Blue Knight is a frequently recurring character acting as a vigilant for robots and sometimes working alongside Astro. He has very similar goals and attitudes but he has a completely different background story and does not transform into any other robotic forms. In this series, he was initially a repair bot at a wrestling arena in space who repaired robots that were badly damaged. After becoming disgruntled by the way robots were being treated, he decides to help them escape but was caught by his human owner Grudon and thrown away in space. Found by Shadow, he was changed into a battle bot. Later on, he takes his followers from Robotonia into outer space to find another planet where they can build their robot nation in complete peace and freedom. In the show, it's also revealed that his real name is Cobalt, as a reference to Astro Boy's brother in the manga and 1963 show, Cobalt.
He is prejudice towards all humans due to his past experience with them, refusing to communicate or listen to anyone and is hostile towards those that have harmed other robots. He also feels no remorse if humans are killed in his attacks nor does he hesitate to destroy other robots who oppose him including. It took Astro a long time for him to realize that humans are not all bad.
Main article: Robotonia
Robotonia is a robot city situated at the south pole that the Blue Knight built for robots. It declared war on humans shortly after.
- He does not appear in the 1980's series. Atlas took his place due to their similar roles and backstories, with the exception that Atlas was made with stolen blueprints. It is worthy of note that the 1980s Atlas can be nicknamed as the "Red Knight".
- His background storyline in the 2003 series resembles what happened to his sister and brother in the manga. Like them, he attempted to help the robots escape from their cruel owner but was caught and punished.
- A reincarnation of him appears on the Gameboy Advance game Astro Boy: Omega Factor. In this game, it is revealed that he is Rag, a former robot servant who was thrown away by his owner Rock. He became the Blue Knight to save all the robots.