WARNING: The following article contains major spoilers for Avengers: Infinity War, in theaters now.
The villains of the Marvel Cinematic Universe vary from simple and boring to complex and impactful, but no matter how great or how bad they are, none of them ever had to meet the high expectations created by six years of anticipation, After all of that, Thanos would either meet that high-water mark or fail miserably when he finally emerged into the spotlight in Avengers: Infinity War.
Marvel Studios President Kevin Feige promised fans in 2017 that Thanos would be the MCU's biggest and baddest supervillain. While it's not unusual for filmmakers to make exaggerated claims to build excitement, Feige's assertion wasn't the kind one makes without absolute certainty that Infinity War would deliver. Still, that wasn't the boldest statement made by those involved with the sequel.
Directors Joe and Anthony Russo intended to create a villain that would leave a lasting impression. At one point, Joe Russo stated, "I wanted to turn Thanos into Darth Vader for a new generation." It was an ambitious goal, but after seeing Infinity War, many fans may agree the Russo brothers could actually have a shot at achieving that, because the Mad Titan certainly isn't the average MCU supervillain.
Until this point, the MCU has developed a reputation for villains that are often generic and occasionally poorly written. There's a broad spectrum of supervillain types in this cinematic universe, and they're not all golden.
A lot of them are, more or less, dark reflections of their heroic adversaries with no real character of their own: Iron Monger (played by Jeff Bridges) in Iron Man, Abomination (Tim Roth) in The Incredible Hulk and Yellowjacket (Corey Stoll) in Ant-Man. None of them had any real depth; they were evil for evil's sake, and were incapable of being anything more than lessons in discipline for their nemeses.
The one time a dark reflection worked well was in director Ryan Coogler's Black Panther, with a primary antagonist Killmonger (Michael B. Jordan) who didn't don a costume similar to the protagonist's until the very end. Killmonger had far more impact than his villainous predecessors, partly because his motivations were complex but understandable.