Bugs Bunny has had numerous antagonists over his long career. Elmer Fudd, Yosemite Sam, the Tasmanian Devil, among others. None have really been a match for him, limited by their modest intellect or rage issues or other fundamental character flaws. The only one who really ever gave Bugs a run for his carrot was not of this Earth. Marvin the Martian, who debuted in the 1948 short Hardevil Hare, was far more competent than the smug rabbit's terrestrial foes, far more technologically savvy, and far more inherently evil. Fudd and the others were hungry or just plain off their rocker, but Marvin was a brilliant strategic genius armed with advanced technology, and on more than one occasion he came very close to the big kaboom he wanted so badly.
What I loved about Marvin was how sinister he was, how quiet and deliberate. That he was from Mars and dressed like the Roman God Mars was a surface pun that the creators took a step further when Marvin declared his intent to remove Earth for a better view of Venus (Mars had an adulterous affair with Venus in the Greco-Roman mythological canon). Still, the viewer was left with the sense that destruction itself was the goal, the more spectacular the better. This was a nihilistic little alien with a plan and the means to carry it out.
Marvin was also known for his pseudo-scientific techno-babble regarding his futuristic weapons. As a sometime purveyor of science fiction technobabble myself, I salute him.