It had to be on here, didnt it? The radioactive remnants of Supermans home planet ended up as his primary weakness, ensuring that even mere mortals could challenge the Kryptonian powerhouse in the right setting. The glowing green rock weakens Superman, while the red variant sees the hero lose his inhibitions. Black kryptonite splits him into a good and an evil version of himself, and the golden variety permanently removes the powers of Kryptonians. Lex Luthor, Batman and Green Arrow have all used this radioactive substance to cripple and defeat the Man of Steel, and it consistently works. It not only sickens the mighty hero, but it causes him to be vulnerable to attacks by humans. The term kryptonite has entered popular language, with the word essentially meaning someones Achilles heel, and it is the most common thorn in Supermans side. Although it isnt quite the most spectacular way to cripple the Man of Steel.