A Race of Evil Shape Shifters, the Sk-Growls had been looking to enslave Earth for many years. One of their earliest invasion attempts was thwarted by the Fur-tastic Four. Who tricked them into believing that Earth was protected by creatures of great power. This was old B Movie monster footage that Lead had shown them.
With the Sk-Growls believing this to be true, they called off the invasion attempt.
It was not long before the Sk-Growls found out they had been duped by the FF..... and when they returned they sent a new threat to battle the FF ..... The Super Sk-growl. (but more of him soon)