In a battle against the Hulk, Thanos admitted he understood why the Avenger is considered a genius on his planet. In Thanos vs. Hulk #2 from Marvel Comics, the Mad Titan and the Jade Giant fight in Bruce Banner's mind. Thanos revealed he was impressed with Banner's intelligence but followed up the surprise compliment towards his opponent with a subsequent dig that somewhat negated the moment of praise from the villain.
As one of the most powerful villains in Marvel Comics history, Thanos isn't afraid to admit how he's truly feeling about someone he's fighting with or against. For example, during his quest to gather the Infinity Stones, the Mad Titan admitted he didn't want to kill the Elder of the Universe, the Gardener, and regretted being forced to do so. Meanwhile, in a different continuity where he fought alongside the Avengers against Annihilus, Thanos shared that he was proud to call Thor an ally. However, one of his more notable compliments came when battling the Hulk, where Thanos revealed what he thought of the longtime Avenger.
In Thanos vs. Hulk #2 by Jim Starlin, Andy Smith, Frank D'Armata, and Travis Lanham from Marvel Comics, Thanos connected inside the mind of the Hulk after Annihilus captured the Avenger. The Mad Titan tries to figure out what the bug king villain is up to, leading him to confront the Jade Giant within his psyche. When Hulk resists giving Thanos any information about why Annihlus captured him, they fight, where the supervillain reveals he was impressed with Bruce Banner, calling him a genius with a reputation that is "well-deserved."
Thanos Knows Bruce Banner Is A Genius
In fitting fashion, Thanos immediately lobs an insult at Bruce Banner after complimenting the Avengers' intelligence. He tells Banner and the Hulk that while he is a genius, it's "solely by Earth standards," saying his own Titan intellect is "another matter entirely." So, while Thanos praises Banner initially, he makes sure to insult him at the same time - which feels very in character for the supervillain. Thanos rarely gives, in this case, a compliment without taking something afterward.
Getting called a genius by Thanos, especially as an Avenger, is about as big of a compliment a hero can expect from the Infinity Gauntlet-wielding villain. In the issue, Thanos recognizes that even for someone from Earth, Bruce Banner is no ordinary human - leading to a brief moment of respect for Thanos towards the Hulk, which quickly fell to the wayside as the two continued on with their fight.