Steve Gerber contributed to the comic, but denied having a hand in the character's creation, crediting it to Seuling.

Due to his parents being affected by radiation, he was born with black skin and tufts of body hair.

[5] While wandering the desert, Jerome encountered Nekra Sinclair, the daughter of the cleaning woman who had been bombarded by radiation in the same accident that had affected Beechman's father.

For six years, they lived by theft and scavenging until they were attacked by a lynch mob that thought they were monsters, awakening their abilities and enabling them to escape.

Traveling to Africa, the two plotted to seize control of three small nations using the Mandrill's pheromones and create a society free of the values that had led them to be rejected when they were young.

[16] Mandrill attempted to avenge the death of Nekra in Los Angeles, California by attacking the Grim Reaper.

[18] Mandrill was incarcerated on The Raft, where he escaped during The New Avengers #1 to join Crossfire's mind-controlling team of villains in Spider-Man: Breakout.

The Hood hired Mandrill as part of his criminal organization to take advantage of the split in the superhero community caused by the Superhuman Registration Act.

[21] When Alyosha Kravinoff (the son of Kraven the Hunter) began collecting a zoo of animal-themed superhumans some time after the "Civil War" storyline, including Mandrill.

[volume & issue needed] He assists the Hood's group in fighting a Skrull invasion force in Central Park.

[34] During the "Hunted" storyline, Mandrill is among the animal-themed superhumans who are captured by Taskmaster and Black Ant for Kraven the Hunter before being killed by robots.