WARNING: The following contains mild spoilers for Avengers #38 by Jason Aaron, Ed McGuinness, Mark Morales, Jason Keith and VC's Cory Petit, on sale now.
In Avengers #38, as Earth's Mightiest Heroes prepare for the start of the "Enter the Phoenix" event storyline, the issue reveals the secrets of Mephisto throughout the history of the Marvel Universe. The demonic character has recently been playing an intricate game: he's been manipulating several parties such as Atlantis, the vampires and the Squadron Supreme to become the Avengers' latest enemies. But his influence actually stretches much further than that.
In fact, it turns out that Mephisto has been the devil on the shoulder of many villains throughout history. He was the one behind the rampage of the Hulk after the team originally united, and he also convinced Apocalypse to attempt to take over the world. What's more, it turns out Mephisto even brought the Mad Titan to Earth, a very long time ago, to face off with the Avengers of 1,000,000 BC.
The prehistoric Avengers were the very first version of the superhero team. Lead by a Mjolnir-wielding Odin, the team was comprised of Agamotto, the Phoenix, the Starbrand, and the firsts Black Panther, Iron Fist and Ghost Rider. They assembled at the dawn of time to defeat a dangerous Celestial. The existence of this team was first revealed in 2017's Marvel Legacy #1, and a few more of their adventures, on their own and as a team, have been revealed since.
Now, Avengers #38 reveals that this original team of Avengers actually fought a young Thanos a million years ago. The comic reveals Mephisto's machinations against the Avengers across time, and it all begins with the demonic character convincing a teenage Thanos to visit Earth, with the promise that it would be a place where the Titan could get closer to Death.
The cosmic villain has been in love with the physical embodiment of Death for a very long time, as chronicled in 2012's Thanos Rising, by Jason Aaron and Simone Bianchi, which revealed the Mad Titan's origin. Now, we know that during that time, Mephisto once approached Thanos and nudged him in the direction of Earth.
Mephisto, who is essentially the Marvel Universe's version of the Devil, immediately saw these first Avengers as a threat to his plans, and the young Thanos was his first attempt to take them out. As a result, the Titan visits Earth during the Stone Age, and he faces Odin and his superpowered team. "Behold, primitives of Earth!" he tells them. "Your new overlord has come! And you may call him Thanos!" This isn't the all-powerful, frightening version of the villain we know -- not yet, at least. Here, Thanos is younger, smaller, and armed with an energy weapon. He appears more naïve, and it looks like he truly believes that his fight will be an easy one.
The confrontation between the young Thanos and the prehistoric Avengers isn't detailed further -- all we know is that the superheroes won, which is obvious considering the levels of power on their side. This adds a whole new layer to the villain and his never-ending rivalry with Earth's defenders. Thanos famously fought the Avengers in 1991's The Infinity Gauntlet, and nearly succeeded in killing half of all life in the universe -- another time when Mephisto was acting as the devil on his shoulder. But now, we know this fight stretches back even further than that -- even if it wasn't the same version of the team. Now, we know Thanos and the Avengers have been enemies ever since the beginning of time.