Warning! Spoilers for Eternals #12 by Marvel Comics
Marvel Comics just revealed the truth behind Thanos' true origin and his parent's creation of the villains, putting him in a new direction in the universe. In Eternals #12 by Marvel Comics, Thanos attempts to reconstruct his body within the Great Machine, where he learns that there is something deeply wrong with him and that he isn't the creature his father and mother created.
In the current Eternals series from Marvel Comics, Thanos has returned from the timestream with his body being a shell of its former self. Desperate to restore (and improve) his body, Thanos sought out his exiled parents for answers, becoming the Prime Eternal to gain the information he needed. Marvel further explored Thanos' inception and creation, as his parents Mentor and Sui-San wanted to prove they could create life - a plan that ultimately cost them their freedom. Now, with Thanos going inside his father's mind, the Mad Titan's true origin is being revealed.
In Eternals #12 by Kieron Gillen, Esad Ribic, Matthew Wilson and VC's Clayton Cowles, Thanos' quest to restore his body and destroy Earth reaches its grand conclusion. Inside Mentor's mind, the Mad Titan finds the answer to how he's been made. However, when Domo tries to make him whole again, he learns the truth about his origin. Domo explains that his parents used Kronos' power to marry Deviant and Eternal material. Despite a connection to the Great Machine, something is wrong with him as "death lies congealing in every part of" Thanos. Domo tells him he's not the creature his father and mother created, as he's become something else entirely.
This Thanos retcon, revealing his DNA was intentionally part Deviant and part Eternal – rather than a fluke because he was born from two Eternals – rewrites his origin. It explains why he could never connect with the Great Machine like other Eternals. Instead, he bonded with death, which actually helps explain the Mad Titan's obsession with it. Thanos admits that even in defeat, he proved himself greater than any of the Eternals, as he evolved into something different - because he is something different.
Ultimately, Thanos' new origin makes sense, as him randomly getting the Deviant gene in his original backstory seemed like it had to be intentional. It turns out, it was. Thanos is the product of an experiment to combine a Deviant and Eternal that went horribly wrong. It's a relatively simple explanation that shows how his parents messed up big time in their efforts to prove Eternals could create life. The revelation about Thanos and his new role will surely be explored in future stories, as the current Eternal series from Marvel Comics concludes with a bang.