Mallah was part of a gorilla troop in Bwunda. In 2008, a thin man and an old woman came to Bwunda and captured him. They surgically enhanced his brain, giving him greater intelligence. Mallah approved of the change and betrayed his troop, helping to capture and enslave them. Brain considered him his best experiment.
While his boss was catching animals to test Kobra-Venom on, Mallah was tasked with keeping people out of the area. He attacked multiple groups, including Hamilton Hill's hunting party, these attacks stirred superstitions among the local tribes.
Brain moved his experiments to Bwunda, and there they were discovered by the Team as well. He watched with his master as the interlopers were caught on security camera. Their ally Ultra-Humanite suggested to send out Gorilla Grodd.
Grodd and Solovar brought the Team, except for Miss Martian and Wolf, to Brain and Ultra-Humanite. Mallah was put to blame for the failure of Grodd and Solovar, as Brain remarked his perfection spoiled him, but also meant Brain was not used to less intelligent apes.
Mallah was with the Brain and Ultra-Humanite while they discussed possible experiments to perform on the captive Team members. After Robin escaped and freed his teammates, Mallah stood ready with his gun. When the fight began, the other gorillas sided with the Team. Solovar took Mallah's weapon and helped Miss Martian to restrain him, allowing Superboy to knock Mallah out.
In the comics, Monsieur Mallah was a member of the Brotherhood of Evil, the right hand (and lover) of the Brain. They were long time villains of the Doom Patrol, until their deaths at the hands of Gorilla Grodd in Salvation Run.
This is Mallah's third animated appearance. He appeared in the final season of Teen Titans as part of the Brotherhood of Evil, and in Batman: The Brave and the Bold (voiced by Kevin Michael Richardson) first as a member of Grodd's G.A.S.P., and later with the Brain.