Kralik was a ruthless interplanetary tyrant that the Silver-Age Superman said was the only villain he faced whom he feared. 

Almost the equal to Superman in powers and abilities Kralik supplemented his powers by also being a master of martial arts and having a ruthlessness that let him do anything.  

While defeated by Superman, he later admitted that this happened only because of a “lucky punch.” Because of this Kralik was the villain he feared.