But what's most intriguing about Thanos isn't that he wants to wipe out half of life across the universe — instead, it's that he's a big purple alien who feels genuine emotion. He cries when he's forced to sacrifice Gamora, his adopted daughter. He feels pain and anguish. But like many memorable bad guys, he believes it's all for the greater good.

Sharp-eyed viewers will notice Thanos looks very different in Infinity War than he did in the Avengers post-credits scene. That's not just due to the advanced in CG technology. "We all came to the conclusion that the performance would actually come through a little bit better if we introduced a little bit more of some of the recognizable features of Josh Brolin," said Kelly Port from the VFX company Digital Domain, one of many effects firms working on the film.

Digital Domain also used a piece of custom machine learning software called Masquerade to make the motion capture performance seem more natural. The process starts by placing 100 to 150 tracking dots on Brolin's face, which is captured by two vertically oriented HD cameras. It's not meant to be a high-resolution scan; instead, it's a fairly low-quality rendering. That's fed into a machine learning algorithm that's using a library of high-res face scans, across a wide variety of expressions.