Cull Obsidian

Cull Obsidian is one of the secondary antagonists of the 2018 Marvel film Avengers: Infinity War. He is a member of the Black Order (alongside Corvus Glaive, Proxima Midnight & Ebony Maw) and an adopted son of Thanos who intends to help him in his quest to search and collect the Infinity Stones.

Role
Obsidian was first seen raiding the Asgardians' ship following the destruction of Asgard by the deceased Surtur. Along with his father and siblings, he slaughtered the Asgardians to their deaths just as Thanos forced Loki to surrender the Space Stone (the Tesseract). It is also revealed that Obsidian was involved of his father's attack on the planet Xandar to gain possession of the Power Stone (the Orb), which he used to destroy Xandar. After Thanos kills Loki, Obsidian escaped with his family as Thanos uses the Orb to destroy the Asgardians' ship, leaving a helpless Thor to drift in space.

With two of the Infinity Stones in place, Thanos sends Maw and Obsidian to Earth, where they laid down an attack in New York City to draw Iron Man, Spider-Man and Doctor Strange into the scene, being aware that Strange has the Time Stone (the Eye of Agamotto) in his possession. Despite the heroes' efforts, Maw managed to capture Strange and flies away on his ship, intending to deliver the Time Stone to Thanos at the planet Titan while Obsidian meets up with Proxima and Glaive following their failed attempt to capture Vision (who has the Mind Stone).

After collecting the Reality Stone (the Aether) from the Collector, the Soul Stone from Red Skull, and the Time Stone (the Eye of Agamotto) from Doctor Strange, Thanos sends Proxima, Glaive and Obsidian to Wakanda, ordering them to lead a massive army of Outriders to attack the country and obtain the Mind Stone at all costs. This forces several Avengers and Wakandan warriors to fight back against the massive army. During the battle, Obsidian engaged into a fight against Bruce Banner wearing a Hulkbuster suit. Though he managed to tear off arm one of Banner's arms, Banner set the arm to flying by activating its thrusters, sending Obsidian into the forcefield protecting Wakanda until he exploded to his death. His siblings and the Outriders would later meet the same fate after being killed the Avengers.

Despite the losses, an arriving Thanos managed to obtain the Time Stone on Titan, and did the same for the Mind Stone after killing Vision. Thanos then used all of the Infinity Stones to wipe out half of the universe's populace (including several Avengers and Guardians), much to the heroes' distraught.