Keisuke Jin is the main protagonist of Kamen Rider X. He was remodeled by his father, Keitaro Jin, into a Kaizorg, a cyborg built for undersea exploration, becoming X-Rider. He is also otherwise referred to by the title Kamen Rider X.

For the first 27 episodes, Keisuke used the phrase "Set Up" and jumps into the air with his bodysuit manifesting as he removes the "Redizer" & "Perfecter" from the sides of his belt to form his helmet and then snap up the faceplate to complete the transformation. From 28 onward, Keisuke uses the phrase "Dai Henshin!" to transform while making an "X" sign with his arms after V3 gives him Mercury Circuit, which greatly powered up X. However, as shown in Kamen Rider Spirits, his original transformation can still be used in the case the Mercury Circuit is out of energy and is yet to recharge. As Kamen Rider X, his power apparently comes from solar and wind energy, which for the Ridol to absorb the energy up to the Mercury Circuit to access the proper transformation.As a Kaizorg, Keisuke is a master of undersea combat.