If you've seen Infinity War, then you know that Thanos is the most powerful being in the Marvel Cinematic Universe. No one else has given the heroes of Marvel quite the run for their money like the Mad Titan. But where does this character come from, and what's the comic book version of him like?
The purple destroyer of worlds--the one that isn't Galactus--made his debut in Iron Man #55 back in 1973. He was created by Jim Starlin and Mike Friedrich. The character was born on the planet Titan and developed a Deviant gene at birth, which changed his skin color but also gave him super-strength and other physical abilities.
Thanos' mother saw a deadly future for her son, so she decided to try and kill him, but failed after being stopped by Mentor of the Eternals, the father of the child. The Mad Titan's lineage may hold some more secrets to his powers. Aside from both his parents being Eternals, His grandfather was Kronos, a character that was essentially a cosmic god with an unbelievable power set, like being able to create other god-like beings from scratch.
Growing up, most of the love and admiration in this family went to Eros, Thanos' brother. The character would later take on the name Starfox and become a member of the Avengers. Because the spotlight was always on Eros, Thanos felt ostracized which led him to other pursuits: murder.
Thanos was gifted academically and was obsessed with figuring out his genetic abnormality, so he began killing animals to learn more about them. He had the help of a young girl who helped him overcome his fear of killing. He then moved onto Titanians, including his own parents, with this girl by his side. Eventually, Thanos came to the realization that this young girl was the physical manifestation of Death, and Thanos became obsessed with her.
His obsession with Death is what drove him on a quest to obtain the Infinity Gems. To appease his mistress, he eliminated half the life in the universe. You can learn more about the Mad Titan, including his powers and comic stories that are a must read, in the video above.
You can see the live-action version of Thanos (well, CGI version), played by Josh "Cable" Brolin, in Avengers: Infinity War and Avengers: Endgame.