Here we have an origin picture of how Maximus got his powers and ability to speak. Maximus lived on a farm as the biggest and strongest horse there, mainly helping do manual labor and such. One day he goes into the barn and finds a hidden project that the farmer owner's son, who was far more brainy, was working on. A real size ray!

But as Maximus got too close, all the energy from the ray glitched out and shot into him, giving him both the ability to speak as well as the power of the size ray, now being able to grow and shrink anything he wants, including himself. Needless to say he puts his new powers to good use, having fun with them and occasionally messing with everyone on the farm using his power, particular Tim, the son of the farm owner. More than once has he found himself reduced to 1 millimeter and put on Maximus' back to go for a ride.

Art by  Vanilla_Beam