The history between Starfox and Thanos is a common one, speckled with tragedies besetting the brother's family and subtle competition between the two. In some ways, the two cosmic beings reflect sibling relationships in the real world: tumultuous yet driven by an insatiable hope for redemption.
Eros, known by his superhero alias Starfox, is a lover of life. Contrast that with a fatally obsessed madman and this Titan family has a recipe for both soapy drama and cataclysmic disaster. Both characters have gained prominence due to their inclusion in the Marvel Cinematic Universe, where audiences may not be as familiar with their comic book relationship.
10 They Lost Their Mother (But From Opposing Sides)
Thanos has a tumultuous relationship with his mother, Sui-San, and for good reason. She tried to kill him as a baby due to his grotesque appearance and remained suspicious of her eldest son up until his invasion of Titan. Eros opposes his brother's invasion and joins with his father, Mentor, alongside Captain Marvel, to repel the attack. Captain Marvel #27 follows the trio in an intense standoff with Thanos' minions, while issue #33 confirms Sui-San's demise.
9 Eros Knows Thanos Is Dangerous
Thanos' first attack on Titan was a wake-up call for Starfox and he subsequently joined up with resistance forces to repel any further attempts at conquering. Having witnessed his brother's aggression growing up, Starfox is consistently reminded throughout the Marvel canon that his brother is a threat.
He bears witness to the events of "The Infinity Gauntlet," where Thanos snaps away half of existence and attracts the attention of Earth's Mightiest Heroes. Most of Eros' adventures involve him, either directly or tangentially, confronting Thanos in some way.
8 Eros Values Life While Thanos Worships Death
Eros is not only Starfox's real name but is also the moniker taken up by the Greek god of love. Similarly, Starfox has the ability to manipulate the pleasure centers of others. Appropriate, given the character's general zest for life. By contrast, Thanos obsesses over his affection of Lady Death and usually finds life inadequate or unworthy. The two are complementary, yet diametrically opposed to each other.
7 They Are Practically Born Enemies
Both Eros and Thanos are Eternals, offshoots of the human race created by the Celestials; however, only Thanos suffers from Deviant syndrome. Instinctively opposed to such beings, the Mad Titan becomes the black sheep of the family. With one son a pure Eternal and another inflicted with the Deviant gene, the dynamics of the family naturally shift to one of uneasy tension. Natural enemies with familial bonds are ripe for comic book drama.
6 They Aren't Above Mundane Brotherly Conflicts
Titans will be Titans. As the two are brothers, they've come to not only inconvenience one another in enormous ways but subtle ones. One of the most passive-aggressive examples is when Thanos grows tired of his brother's constant nagging during the events of "The Infinity Gauntlet."
Eros is forced to watch as Thanos gradually wipes beings from existence and desperately attempts to talk his sibling out of it. Thanos simply erases his mouth, continuing with his torture.
5 Thanos Is Incapable Of Loving Eros
Starfox's persistence as a hero is matched only by his brother's penchant for evil. She-Hulk #12 sees Starfox attempting to clear his name of sexual assault allegations via a Titanian trial. Thanos appears to testify that his younger brother inspired his love of Lady Death; it's revealed later that all of Starfox's memories used against him in the trial are fake, implanted by Thanos to frame his brother. This demonstrates the tragic dynamic of the siblings: Thanos is forever scheming against others who threaten his monopoly, therefore incapable of reciprocating his joyful brother's love.
4 Eros Tried To Keep Thanos Dead
Thanos #1-18 sees the Mad Titan wrestling his mortality after a long hiatus from the universe. Thanos' son Thane recruits the Champion of the Universe and Starfox to take advantage of his father's weakened state and kill him. They succeed, but not without some unintended consequences. Chief among them is the birth of a new threat in Thane, having been possessed by the Phoenix Force. Starfox didn't succeed in completely eliminating the threat, but the story cemented the character's awareness of his brother's dangerous tendencies.
3 Starfox Has Fought His Brother's Children
Following the Phoenix Force's possession of Thane, Starfox finds himself at odds with one he had fought alongside not long before. Thane falls prey to the whispers of Lady Death, akin to his father, and brings destruction wherever he goes.
The well of evil rarely runs dry in the bloodline of Thanos, leaving a legacy that subsequent generations must contend with. Even though his brother is seemingly defeated, Starfox continues to wage war on his ideology.
2 They've Been On The Same Side
Desperate for victory in the battle against Thane's massacring, Starfox calls on a greater foe: the original Mad Titan himself. Thane believes his father was destroyed, though he inadvertently banishes him to Titan instead. Given the circumstances, Starfox finds it constructive to bring Thanos into the fight against his progeny. The alliance does not last, as Starfox and his allies find themselves deserted by his brother in the end.
1 Thanos Possessed Eros
Gamora's slaying of Thanos left a lot of unanswered questions regarding the Mad Titan's legacy. In Guardians of the Galaxy, Starfox sets out to find his brother's body and discovers his will, which predicts Thanos' resurrection in an unknown host. Though Gamora is initially assumed to be the most likely candidate, Thanos ultimately returns in the body of Starfox. He takes control of the Black Order and attempts to reunite with his own body, though meets his end for a second time by Gamora's blade. Robbing his brother of any semblance of self, Thanos demonstrates why the two have such a rocky relationship.