The Sun Monsters are a series of sentient beings based in solar fire. They come from another unknown Universe and have the power to convert humans to their own kind. Generally, they are found to lead invasions with three leaders. The extent of their power is unknown but they pose a significant threat to the Zapbots and more so to humans.
The Sun Monsters attempt to take over Earth but are stopped by the power of the Matrix of Leadership.
After lying in wait for several months in Earth's sun, regenerating the Sun Monsters head towards Earth to destroy it. Gearatron in robot form is successful in destroying them for good, using the power of the Matrix.
Behind the Scenes
Many years later I realize I might have subconsciously recreated Kreemzeek here...