After the Avengers created an alternate timeline in 2014 in their quest to steal the Orb and the Soul Stone, the 2014 version of Thanos used reverse-engineered Pym Particles and a Quantum Tunnel to transport himself, his weaponry and his allies to 2023, including the Chitauri Gorillas. Thanos' entire army was summoned to the ruins of the Avengers facility by Thanos after battling some of the Avengers.
However, when Thanos seemingly was going to win again, all of Thanos' victims came back to life and the ultimate battle for the fate of the universe took place. Alongside their fellow alien soldiers, many Chitauri Gorillas ended up losing their lives against the Avengers' forces. However, the battle came to an end when Thanos attempted once more to use the Nano Gauntlet, only for Iron Man to use the Infinity Stones, causing Thanos' army, including the surviving Chitauri Gorillas, to fade away into nothingness before Thanos himself turned to dust.
The Chitauri Gorillas, as their name suggests, are large alien beasts whose posture and gait resembled that of a gorilla. They have 4 fingers on each of their hands, while their feet have 3 toes. Much like the other Chitauri forces, their bodies have been outfitted with cybernetic implants and armor plating. Some of the armor appears to cover their mouths and obscures their faces. As such, lights on their faces function as their eyes, which shut off after their death.
The Chitauri Gorillas function as military animals for the Chitauri. Despite their large sizes and strength, they seem to be completely subservient to them, seeing as they allow themselves to be leashed by chains.