The Skeletron Drone Series is a line of drones that were manufactured on the planet Ovenga in the Alternate UUniverses. With the increasing popularity of the Starbot Drone Series being reprogrammed by dozens of pirates, an exiled professor named Professor Torowlski began producing factories and using the metals leftover from the planet's many junkyards to begin producing robots programmed for one purpose: piracy. And it quickly became a popular trend. These robots are primarily known for their skull-like heads. Some of these machines are similar in appearance to Terminators, being of a skeletal appearance. Others are remodeled to be stronger and less fragile.
The Model-100 Skeletron is the earliest model. It is similar in appearance to the Terminator, but is much more reinforced and has some strong mechanical structures. However, they are still very fragile and can break when given enough damage. They are the least-used models in the Skeletron series.
The Model-400 Skeletron is much more fit for piracy and combat than the previous model. The skull-like head still remains, yet it's body has an actual base and it's limbs are much more reinforced. They are the pinnacle of the Skeletron series, and can hold it's own against enemies of all kinds.
The Model-700 Skeletron is much different than the last two models. It is not coated with an artificial super-plastic that can survive a lot of damage, and actually makes the model waterproof. It still has the base torso of the M-400, but the super-plastic skin can protect vital machinery from significant damage.
The Model-1000 Skeletron is the rarest of the Skeletron series, and incredibly expensive. They are tall bulky machines that have a stronger base torso, have small traces of super-plastic skin, have skull-like heads, have powerfully-built limbs, and have hardly any weak spots.