WARNING: The following articles contains spoilers for Eternals #1 by Kieron Gillen, Esad Ribić, Matthew Wilson and VC's Clayton Cowles, in stores now.
After the Eternals were all killed in 2018's Avengers #4, Marvel's powerful family of cosmic characters is brought back to life in Kieron Gillen and Esad Ribić's Eternals #1. The issue focuses primarily on Ikaris, who returns to life thanks to the Machine, a powerful technology that can resuscitate fallen Eternals. Almost as soon as he is back, Ikaris gets instructions from Zuras, the Eternal Prime, leader of the race of super-powered beings.
Ikaris goes on his mission to liberate fellow Eternal Sprite and, after the two of them deal with a rampaging Deviant, one of their primordial enemies. But when they return home to Olympia, they discover that something terrible has happened: Zuras has been murdered, and his head has been crushed by the hand of a powerful assailant. Ikaris and Sprite quickly follow the trail of Zuras' killer and, as the issue comes to a close, they find the culprit: Zuras was killed by Thanos, who was seemingly dead before this issue.
Thanos has been a plague on the Marvel Universe for decades. However, his menace finally came to an end in the 2018 event series Infinity Wars, where he was killed by his adopted daughter, Gamora. While the Mad Titan's death came as a total shock, his influence would stretch into 2019's Guardians of the Galaxy series, where the villain's "Final Gauntlet" would reveal that he had a plan to be brought back to life in the body of his brother, Eros. Thanos' enforcers, the Black Order, as well as the Asgardian Goddess of Death, Hela, all joined forces in an attempt to bring the fallen Titan back. However, thanks to the intervention of the Guardians of the Galaxy, a black hole bomb was detonated inside the new and incomplete Thanos and he would disappear into the vortex.
But now, in Eternals #1, Thanos is officially back. Ikaris and Sprite find Thanos in the remains of Titanos, the once-great capital of the Eternals.
When Thanos reveals himself, he appears to be weakened. His armor is beaten and torn and he has tubes connected to an unseen source. Whatever is going on with the Mad Titan, it appears he has not been fully and properly restored yet. For the time being, the most important question is whether this is the Thanos that disappeared in the black hole in Guardians of the Galaxy or a Thanos who has found another way to return to life.
Given that Thanos returns to life nearly at the same time as Ikaris, and considering his involvement in the Eternals series, it's possible that he was brought back through the Machine too. After all, A'Lars and Sui-San, Thanos' parents, were both Eternals, so the Eternals' Machine may recognize Thanos himself as an Eternal on a genetic level. Moreover, Thanos was able to kill Zuras, his uncle, by traveling through the Eternals' teleportation network, something that should be accessible to Eternals only. If the network can treat Thanos as an Eternal, then perhaps the Machine can as well.
For the time being, it's not yet clear how Thanos has returned to life, but it's clear that he intends to kill the Eternals and bring death to those who seemingly can't be killed for long. This is entirely on-brand for the character, who in the comics has a long history of fascination with the living embodiment of Death. To bring death is Thanos' ultimate purpose, and it's likely he sees the Eternals as the ultimate aberration, one that he is intent on finally correcting.