The Blood Brothers were large twin ape-like aliens originally in the service of the conqueror Thanos, acting as the guardians of his first base on Earth. Pursued by Drax the Destroyer, the duo battled the superheroes Iron Man and the Thing in a bid to stop them from interfering in Thanos' plans. When they failed to do so, a disgusted Thanos teleported the Blood Brothers away.
They reappeared years later on Earth in the service of the villain The Controller. Again they battled Iron Man, who defeated them with the aid of the hero Daredevil. Sometime later, the United States military discovered Thanos' old Earth base, and after activating some of the machinery they accidentally teleported in the Blood Brothers. The two battled the Avengers and were eventually depowered by Thanos' brother, Eros.
The Blood Brothers were imprisoned, but were later released by the hero Quasar and left on the planet Mars.
Later, they attempted in vain to stop Rogue of the X-Men from rescuing a mutant extraterrestrial of the Skrull race. The brothers later fought with Earth's many of Earth's superhuman heroes and villains against an invasion by Ego the Living Planet.
The Blood Brothers appear in the Avengers Assemble episode "Hulked Out Heroes", voiced by David Kaye and Liam O'Brien. They ambush Hulk at the top of Stark Tower until Captain America, Falcon, Hawkeye, and Iron Man arrive. When the Blood Brothers have Hulk pinned down, they attach a device to Hulk's back that siphons Hulk's gamma energy which caused some of the Avengers to be infected with an unstable gamma energy virus. The Blood Brothers contact Red Skull to tell them that their mission was a success. Red Skull cuts off the call from the Blood Brothers when they start to ask about their payment.