If you think the Mad Titan of the MCU looks menacing, you haven't been subjected to much of Thanos in Marvel comics. Some unspeakable atrocities have been committed against Thanos himself, but the worst things Thanos has ever done makes those incidents look like tickle fights.
Marvel's Ultimate Universe has depicted all kinds of unsettling things, but the most disturbing Thanos moments in Marvel comics don't even depend on that alternate, gruesome reality (and that's not even considering his evil henchmen, the Black Order).
You might also like this list of the best Thanos story arcs in comics.
Thanos was separated from his mother, Sui-San, as an infant after she sensed the evil inside him and attempted to kill him. They did not reunite until Thanos was a full-grown adult, and as we learn in his 2013 run, Thanos Rising, their reunion didn't go well for Sui-San. Thanos dissects his mother (who was alive at the beginning of the process) in an attempt to discover an explanation for his abominable nature.
In case you were wondering, the sound a head makes when it is squished between two massive hands is "SPLORT." At least, that's how it's depicted in Thanos #10 when the Mad Titan kills Falcon-turned-Captain America, Sam Wilson.
The Thanos comic that began in 2016 goes to some pretty wild places, including a distant future in which Thanos is king of the universe after defeating the Avengers. Most of those Avengers are dead, but not Bruce Banner. He gets the dubious honor or being turned into the Mad Titan's madder hound.
Thanos keeps Hulk in a pit of bones, when he's not on-leash. Among the bones are those of Steve Rogers, the former Captain America who was fed to the Hulk Hound.
The Infinity Gauntlet sees Thanos wreak havoc on pretty much everyone in the Marvel universe. He inflicts the most pain on his self-proclaimed granddaughter, Nebula. When the space pirate makes this claim of relation to Thanos, the Mad Titan repays her by transforming her into "a hideous living sculpture of pain and living death."