Beastmen are the primary antagonists of the first half of Gurren-Lagann. They are a blend of human and animal DNA, varying greatly in appearance; some are almost completely humanoid, while others are entirely inhuman-looking. These hybrids served Lordgenome, their creator. They cannot produce Spiral Power and, as such, do not set off the Human Extermination System set up by the Anti-Spiral. They also cannot reproduce and need coma-like sleep to stop from cell degeneration, unless they have an immortal body like the one given to Viral. Due to their inability to produce spiral power, they pilot Gunmen by using solar powered batteries, which prevents them from operating at night. However, larger Gunmen (such as Dekabutsu or the hot spring gunmen) can supply smaller ones with power, allowing the Beastmen to work at any time of the day.
They do not like humans and see themselves as superior to them because of their rule over their Earth under the Spiral King, who had them kill any humans who made it to the surface. The Human Extermination Army was divided into 4 divisions, each ruled by a different Supreme General.
After Lordgenome's death, the Beastmen armies were disbanded and all Gunmen were scrapped. Many Beastmen living within Teppelin itself survived its collapse, and were persuaded by Nia Teppelin to accept peace with the human victors and were integrated into Kamina City's society without prejudice. On the outskirts of civilization, liberated Beastmen warlords continued to wage campaigns against human settlements, so battles between the New Government and Beastmen erupted over time. Seven years following the Battle of Teppelin, few if any of these resistance forces remained, most having been eliminated by Grapearl squadrons.