He was born on planetoid LV-223, and was a ninja the second he was born. He then joined the other Teletubbies, killing people, an hour after he was born. This is because he felt like it, thus he was crowned the award for beating people up.
He is very close to Po, or so he thinks. Po has no heart, but Ninja Teletubby still thinks they are friends. Po is the only person that can trick the Ninja Teletubby.
He might be Japanese due to his ninja fighting style. He might have also killed Barney. He is the most skilled Teletubby.