How do you top a Kryptonian with super strength, speed, stamina, flight, heat vision, freezing breath and nigh invulnerability? Easy! A martian who can do all those things, and more!
J'onn J'onzz is Martian Manhunter, a being who even Superman said: "He is the most powerful being on the face of the Earth". - JLA #80
I really like the character of Martian Manhunter. He's got a gentle, compassionate personality as well as being very badass in his ability to do...just about anything! Super-everything, invisibility, shape-changing are just a few of his powers. Like Supes, they had to sneak in ONE weakness, which is fire...because! Later on, writers created this as a built-in psychosomatic effect to J'onn's race in order to prevent them from regressing to a more domineering, aggressive, conquest-type of race. They later removed this weakness completely. Oh, writers!