First, it should be noted that comic books and movies are a very different medium and certain things that work well in comic-form would be rather silly on screen. There are some aspects of Thanos in Avengers: Infinity War that aren’t in the comics but work really well.  And there are also some aspects of the character in the comics that are great, but wouldn’t work on film.  Neither interpretation is necessarily superior, they’re just different.  Comics have also been around for many decades so a lot of authors have had a hand in writing and creating the various characters.  This means that very few characters in the comics have been consistently written for their entire existence.  Whereas in the MCU, there’s a very clear continuity beginning with Iron Man in 2008.

Motivation

As many have acknowledged, Thanos in the comics is largely motivated by his love for the physical embodiment of Death.  In order to win her favor, Thanos pursues the Infinity Gems so that he can prove his love by giving her half the universe.  But he’s ultimately unsuccessful and throughout his entire comics history, his love for Mistress Death has never been reciprocated.  In fact, at one point she makes him immortal so that he can never feel her embrace.  In Avengers: Infinity War, Thanos is seemingly motivated by an altruistic goal: saving the universe from overpopulation.  The deaths he’s caused have been in the pursuit of saving the universe’s finite resources.  This is a more realistic and understandable motivation.  Even though his love for Mistress Death is more well known, Thanos in the comics is also concerned with overpopulation.  Before the famous Infinity Gauntlet saga, Thanos has a conversation with the Silver Surfer where he explains the dangers of overpopulation:

Science and a benevolent nature have allowed thousands of different species to flourish beyond the capability of their environs to sustain the.  The grand design has been thrown off kilter.  If left on their own, this universe’s races will squander their riches and perish within a few centuries.  The pendulum will swing from one extreme to the other.  From an overabundance of life to no life whatsoever.  My Mistress Death likes a constant and steady harvest, the balance must be maintained.

So even though Mistress Death doesn’t play a part in Avengers: Infinity War, his motivation is still somewhat inspired by the comics.  His love for Mistress Death is also an example of something that works better in a comic book than it would on screen.  Overpopulation is a much more concrete idea than a love for the physical embodiment of Death.  Instead, in Avengers: Infinity War, we see the love he has for his daughter Gamora.  Just like in the comics, where his love for Mistress Death is quite twisted, his love for Gamora is also very tragic.  She’s the one person Thanos cares about, but not enough to forgo his delusional goal.

Characterization

In the comics, Thanos is depicted as a maniacal warlord with a huge evil grin.  And he’s almost always wearing his iconic gold and blue armor.  But because he’s depicted as more sympathetic in Avengers: Infinity War, Thanos loses his armor and some of his maniacal qualities.  It’s also explained because as he gets more powerful throughout the film, Thanos no longer needs the extra protection.  As for his villainous persona, toning some of that down makes for a more believable character.  Even though you may understand where Thanos is coming from in the comics, you never really sympathize with him.  By structuring the film around Thanos you understand why he makes certain choices because they’re for believable reasons.

While he’s incredibly intelligent, as evidenced by his conversation with the Silver Surfer, he has a much more unhinged personality.  We see a bit of this in the opening when the Black Order goes to help Thanos fight the Hulk, but he’s stopped by the Ebony Maw who says, “Let him have his fun.”  This fits in quite well with what we’ve heard about Thanos in the past.  In Guardians it’s mentioned that he’s a terrifying warlord, so perhaps in his younger days Thanos was a more evil and selfish ruler.  And it’s only now that he’s older that he’s adopted a more altruistic justification.  Which is nice that they’re acknowledging the character’s maniacal comic roots while making him a more complex character.

One other important characteristic of Thanos in the comics is his hubris.  Thanos is incredibly confident in his abilities and believes that he’ll be victorious no matter what.  Of course, a big reason for that is because he’s collected the Infinity Gems and becomes (quite literally) the most powerful being in the universe.  But that self-confidence is what ultimately brings Thanos down.  He believes that The Avengers are such a small threat that takes off the gauntlet to prove his might.  And he’s not wrong, they don’t stand much of a chance against him even without the gauntlet.  But while engaged in combat with The Avengers, his daughter Nebula puts on his discarded gauntlet and reverses all the damage Thanos has done.  Thanos sows the seeds of his own defeat.

Even though there are some key differences between Thanos in the comics and his onscreen counterpart, Avengers: Infinity War remained quite faithful to the character.  While his infatuation with Mistress Death is quite important in the comics, it makes such a fantastical film feel a bit more realistic.  And now going forward into Avengers 4, it’ll be fascinating to see how (or if) his hubris will be addressed.  It’s a key part of who he is in the comics and makes for a great solution to defeating a character who’s so immensely powerful.  Going into Avengers: Infinity War many fans were worried about Thanos not living up to their expectations, but I think it’s now safe to say that the Russo’s have certainly done him justice.