One-One is the deuteragonist of Book One, a supporting character of Book Two, and the overarching antagonist of Book Three in the Cartoon Network series, Infinity Train. He is the robotic companion of Tulip Olsen who is trying to help her find a way back home. One-One can split into two halves, each with its own personality. The two halves are called Sad-One and Glad-One by the production staff, but as a single unit, they are called One-One. One-One is also the true conductor of the Infinity Train and regains his position at the end of Book One.
Glad-One is voiced by Jeremy Crutchley and Sad-One is voiced by the show’s creator Owen Dennis.
One-One is a white, spherical robot with a black stripe that runs down the entire circumference of its body. On the front, the black stripe has two white dots that appear to be Sad-One and Glad-One's eyes when they are fused. One-One has four retractable spider-like legs.
The body can easily separate into two identical and independent parts and can reattach itself together again. Each half is semi-spherical in shape with a black line at their base with a single white dot, their eye. The flat base of each half has four spider-like legs, similar in structure to when it was whole.
- One-One is the most recurring character in the series, although Samantha/The Cat is the only one to fully appear in all 4 seasons.