Thanos has been lurking in the shadows of the Marvel Cinematic Universe ever since the end-credits tag in The Avengers, and he's expected to wreak havoc on the entire galaxy when both Avengers: Infinity War installments hit theaters in 2018 and 2019, respectively. However, according to Joss Whedon, the Mad Titan may not be the only one going up against Earth's Mightiest Heroes and the Guardians of the Galaxy when the time comes to finally step off of his throne.