Everyone loves an underdog story but there are some comic book fights that really strain credulity. This is especially true when said opponent is Thanos, the Mad Titan himself. Characters of a cosmic scale like the Silver Surfer, Thor and Captain Marvel are comparable in power and might to Thanos, and thus able to provide him with a real fight. However, in one story, Ka-Zar, Lord of the Savage Land, actually took down Thanos -- sort of.
Also known as Lord Kevin Plunder, Ka-Zar wound up being raised in the Savage Land and became its resident jungle lord. The character is largely Marvel's homage to Edgar Rice Burroughs' classic hero Tarzan of the Apes. He's a strong, athletic human being in the prime of his life but far from the most powerful hero on Marvel's roster. For instance, Spider-Man is capable of lifting about ten tons, which is roughly the weight of a car. Ka-Zar is a buff fellow who's handy with a knife and wiry in a fight. Thanos is, to put it mildly, considerably more powerful.
In Ka-Zar #11, Mark Waid, Andy Kubert and Jesse Delperdang built towards a confrontation between the title hero and a mysterious figure working behind the scenes with Ka-Zar's nefarious brother, Parnival Plunder. Their plan: Seize control of the terraforming machinery that allowed the prehistoric environment of the Savage Land to exist beneath the Antarctic ice. The equipment was moved to New York, and Parnival transformed the city into a Manhattan-sized Savage Land. Parnival's mysterious benefactor turns out to be Thano, and so the jungle hero finds himself squaring off against one of the heaviest hitters in the Marvel universe.
The fight was actually more of a running chase, with Ka-Zar doing his best to stay one step ahead of the Mad Titan, who had been using the terraforming technology to restore his waning power. Once clear of the restorative power of the machinery, Thanos' energies began to flag once more, and in an effort to restore them he tried to re-enter the terraformer, only to have the machine destroyed by S.H.I.E.L.D. before he could restore himself.
The story itself features a lot of extenuating circumstance that allow Ka-Zar to defeat Thanos. Needless to say, this victory and others like it did not impress Thanos co-creator Jim Starlin. The writer retconned Thanos' defeats, revealing his enemies had, in fact, only defeated a legion of clones he'd created to act as his agents. Thus, Thanos had not suffered an ignominious defeat at the hands of a mere mortal.
So Marvel's weakest hero didn't actually defeat Thanos after all, but rather a clone of the galaxy's most notorious villain. Still, it can be argued that a clone of Thanos isn't anything to sneeze at either, and for a guy in a loincloth with only a boot knife Ka-Zar didn't do too badly. Still, he shouldn't look for a rematch anytime soon.
Next: Ka-Zar Wanted Only ONE Weapon From Black Panther - Here's Why