Today Thanos is a household name, but back in May of 2012 he was virtually unknown, except to hardcore Marvel fans. When he first appeared in the MCU in the first post-credits of the first Avengers, his menacing smirk at the prospect of courting death left many scratching their heads. Then the shawarma-eating sequence drove the question temporarily from their minds until they left the theater and Googled "Who the hell is the purple dude at the end of Avengers?"
While Thanos' tiny cameo set the MCU on the road toward the shocking events of Infinity War, director Joss Whedon recently admitted that he had no clue how to handle the villain. In fact, the Thanos you see in the third Avengers movie was not originally concocted by the Buffy creator.
“Honestly, I kind of hung [Thanos] out to dry,” Whedon told IGN. “I love Thanos. I love his apocalyptic vision, his love affair with death. I love his power. But I don’t really understand it. He’s had a lot of power, and he was cool in the comics. And I’m like, Thanos is the ultimate Marvel villain! And then I was like, I don’t actually know what I would do with Thanos."
In the comics, Thanos is obsessed with not just the concept of death, but the physical embodiment of it. To impress her, he kills off half the universe with the Infinity Gauntlet in Jim Starlin's famous Infinity Gauntlet saga, which heavily influenced the storyline of Infinity War. However, screenwriters Christopher Markus and Stephen McFeely decided to alter the character a bit by making him the sole survivor of a planet that drove itself to extinction via overpopulation and, by extension, depletion of resources.
Within the MCU, Thanos (played by Josh Brolin) wants to wipe out half of all life in the universe, not because he's got a sick fascination with death, but because he wants to save it and the only way to do so is to prevent the expansion of life. In other words, death is not the end goal, but the means to an end. This change to the Mad Titan's core drive is something that Whedon admired.
"I liked what [the Russo brothers] did so much, and I thought Josh Brolin killed it," he continued. "And they did an amazing job of keeping that performance on-screen ... I thought they did what they needed to do. [Thanos falling in love with Death is] not a concept that will necessarily translate. It’s sometimes also an easy out for a villain. To say, I love destruction! No, really, I’m in love with it. And yet, you’re still just a nihilist. Whereas they gave him an actual perspective and made him feel righteous to himself, which is always a better idea. So I liked what they did very much. I did not know about it, I certainly didn’t come up with it.”