As you can probably tell from the picture, Spanner is a robot. He fell out of a tree as a child, breaking all the bones in his body. There was no way he was going to survive, but moments before death he managed to build a robot body out of nearby scraps of metal. Spanner got his brother to put his brain into the robot body, and miraculously he has managed to live as a robot ever since. This young genius invented all of the squirrel's wargear and the rabid squirrels would have been primitive without him.