Full Name: Unknown
Ranger Destinatiion: Gosei Knight
Weapons: Leon Laser
Gear: Leon Cellular
Headers: Skyon, Sealeon
Gosei Knight as originally the Groundion Headder. Ten-thousand years ago Groundion Headder battled the Yuumajuu until he was separated from his Gosei Angel allies. Stuck within a glacier, Groundion made a agreement with the Earth itself as it gives him the opportunity to presume his human-like form to fight the revived Yuumajuu and cleanse the Earth of any threat. He doesn't care about the humanity of the Earth so this puts him in the odds with the Goseiger. When Gosei Knight first appears, it is reported that the Gosei Knight has no record of him. Unlike the Goseigers, Gosei Knight uses the incomprehensible Knightick Power, enabling him to use the abilities of the Skick, Landick, and Seaick Tribes. When fighting, he refers to himself as "The Earth purifying knight of destiny! Gosei Knight."

Thanks to friendship with Goseiger's young friend, Nozomu, he started to learn the worthy of humanity and that protect them is protect the Earth. So, he takes Goseiger's mission as his own and started to fight alongside the Gosei Angels, assisting them when needed. In the present days, the own planet started to get weaker due the polution. Feeling that, the Earth grants to Groundion its power so he passes for a "super evolution" becoming Gosei Knight, the knight fated to clean the world.

However, Knight didn't want to get along with the Goseiger at first. Knight started to wander around the planet in search of what is polluting the planet. He started to attack the human beings and getting in confront with the Goseiger. When Uobouzu of the Nessie, a Yuumajyu that, in the past, has defeated Groundion appears Knight managed to defeat it with the help of the Goseiger. Since then, he started to respect more the heroes and fight alongside them. After the Yuumajyuu have been defeated, the Matrintes appeared. At first, Knight was attacked by the Matrintes but was saved by Nozomu. After this incident, Metal Alice has tried to induced him to join the Matrintes, since the Matrintes' goal didn't conflict with Knight's as the Yuumajyuu did. So, Knight started to be undecided about what to do. However, thanks to Nozomu and the Goseiger's hard work, Knight was conviced the worthy of human's life and decided to protect them no matter how.

Since that day, Knight and Nozomu had become good friends, with Knight starting to learn more about the humanity and about the humans' feelings. He started to act as a brotherly figure towards Nozomu, giving him support when Alice almost destroyed the train where his mother was (after that, it was revealed that Nozomu's mother wasn't in the train). When Robogog called the Goseiger for a final fight, Knight went with them. Using Bladerun of Cyborg, Robogog managed to seal Goseiger's Tensouder and Knight's LeonCellular. When it looked like the Goseigers was about to be beaten, Knight found out that he still could feel a reaction on his LeonCellular. So, he used the Trianglobal Card in order to stop Robogog of using his Misfortune Destruction on the Goseiger. After, exhaust his gosei power, Knight uses his remaining strenght to restore Goseiger's tensouder.

He is brought to Nozomu's house, when a mysterious light restore a bit of his powers. This light is later revealed as Master Head, who didn't vanish after save the Goseiger from Makuin's dark dimension. So, Gosei Knight went with the Goseiger and helped them to defeated Robogog in his giant form. After the Matrintes are defeated, Bladerun reveals he got back his memories, which was stolen by Robogog. He also reveals he was the one who let a little reaction on Knight's LeonCellular, as part of a plan to destroy Robogog. After this events, Brajira reveals his true face: Brajira of Savior. It's also revealed that in the past, Brajira was Groundion Headder's master and the one responsable for he being in the Glacier. At first, Knight tried to fight against Brajira, however Brajira managed to Kidnap Knight and use his dark gosei power to brainwash him, turning Knight into "Dark Gosei Knight of Groundion Headder". At Brajira's side, Knight started to attacked the Goseiger. However, Alata manage to bring Knight back to his sense, after making him waste tons of dark gosei power while fighting with him. Back to Goseiger's side, Knight tried to attack Brajira's on his base, but failed.

In the final battle, Knight helped the Goseiger by trying to stop one of Brajira's wedges, that would serve to complete the ceremony "Nega End" that Brajira was using for destroy Earth and re-make it as he pleases. When Brajira was defeated by the Goseiger, Knight departed back to the Glaciers, in order to restore his exhausted Gosei power.