Thanos and Darkseid are two of their respective publishers' most powerful villains, carrying out acts of unspeakable evil on a cosmic scale. Both were created around the same time and both had similar looks, making comparisons inevitable. Debate has raged over who is the most effective of the two, and while both have cut multiple paths of destruction across their universes, Darkseid is by and large the scarier of the two.
Darkseid first appeared in, of all places, Superman’s Pal Jimmy Olsen #134 in late 1970; he was created by the legendary Jack Kirby. Thanos debuted almost three years later, in Iron Man #55 and was created by Jim Starlin. Starlin had admitted in interviews that the character designs for Thanos were based on Darkseid, and characters do bear a strong resemblance to each other. Both of them are intergalactic tyrants with vast armies at their disposal. They both have goals of genocide and domination; Darkseid seeks the Anti-Life Equation, which saps free will and Thanos wishes to win the favor of Death by killing half the universe’s population.
Since their introductions, both Thanos and Darkseid have waged war on the universe, and in Darkseid’s case, the Multiverse. Each has tasted victory on more than one occasion. Darkseid almost brought DC’s Multiverse to its knees in Final Crisis and perhaps Thanos’ greatest victory came in the Infinity Gauntlet, where he used the six Infinity Gems to kill half the universe’s population. The two of them have fought nearly every major hero in their companies’ universes as well.
But where Darkseid pulls ahead of Thanos is how difficult he is to beat. To be certain, Thanos is an extremely dangerous foe, and when the heroes do turn him back, it is usually by the skin of their teeth, but Thanos has one huge weakness Darkseid lacks: emotions. Thanos’ desire for Death’s affections drove many of his genocidal schemes, including assembling the Infinity Gems. These emotions are also his downfall: in addition to wanting Death’s love, he has clear personality flaws and smart heroes can use this against him. For example, in Infinity Gauntlet, Thanos was so assured in his victory he let his guard down long enough for Nebula to snatch the Gauntlet away. Adam Warlock foresaw something like this and made it part of his plan to defeat the Mad Titan. No such insecurities exist in Darkseid, making him far more difficult to beat. Indeed, many of Darkseid’s defeats came about because of a special device or gadget, such as the god-killing gun Batman used in Final Crisis. Furthermore, Darkseid is depicted as a dark and evil god—in the acclaimed Mister Miracle maxi-series, Darkseid’s acolytes simply said: “Darkseid is—.” Thanos is just an extremely powerful alien.
Part of Marvel’s approach to characters is to humanize them and give them flaws and personalities, as Thanos best shows. He is like Darkseid but with issues, big issues that ultimately lead to his defeat. Without this key weakness, Darkseid is far scarier villain.