The Grox Leader is the main antagonist of the 2018 live-action/computer-animated film, It Came from the Forbidden Planet.
He is voiced by Harry Shearer, who also voiced Mr. Burns, Waylon Smithers, Reverend Lovejoy, Ned Flanders, Seymour Skinner, Reverend Timothy Lovejoy, Dr. Julius Hibbert, Jasper Beardley, Lenny Leonard, Officer Eddie, Rainier Wolfcastle, Kang and Itchy from The Simpsons.
The Grox Leader tells all of the Grox that they finally destroying many planets, announcing they are going to invade Earth as their new home. He secretly sends Epic Cornelius to kill all the monster tribe's chiefs.
The Grox Leader kidnaps all of the humans from Earth, and succesfully takes over it, and tries to feed the humans to Poultra, a humongous alien chicken whom he and his people worshiped for centuries, or his henchmen.
In the year 3028 AD, he ordered his drones to destroy the planet Earth. Their attempt was successful, although several humans managed to escape into space.
Many years have passed and the Grox Leader and his drones spotted humans at Tau 14. At the planet of the Gaol, she captures Cale Tucker and Akima Kunimoto and imprisons Cale and sends Akima off into space, but Cale manages to escape and meet up with the crew of the Valkyrie. When the crew of the Valkyrie discover the location of the Titan, Joseph Korso, the captain of the Valkyrie, and his first mate Preed betray their comrades by exchanging the location of the Titan for cash from Susquehana.
The Valkyrie's crew arrived at the Titan near an ice ring to destroy the Grox and create a new Earth. As the Titan activates, Susquehana and the rest of her Drej army were incinerated, as their bodies were made of energy, but the Grox Leader survives and escapes.
After he comes to Earth, the Grox Leader reveals himself to be the embodiment of "every chaos where he lurks". He began corrupting Gumbald's soldiers and turning them into a monster. The monster battles with New York and Gumbald's army. When the fight continues, Chief distracts Betty's meditation and Cornelius swallows them. Finn also follows them, and he loses his robotic arm when Cornelius closes his jaw. The Grox Leader also mutates a Gumball Guardian into another monster.
The Grox Leader begins to digest them, by reverting them back to their past selves (except Finn), Simon and Betty reunited once again, as they embrace each other as space they are trapped in begins to shrink. With the bulk of monsters defeated, the Grox Leader, refusing to accept defeat, furiously causing havoc in Earth. T.V., transforming into his blue form, tries to steal the dinosaur embryos, but the treehouse is destroyed inside. Chief is devastated after seeing the wreckage but is comforted by his older son, Chief II, who has suffered flatuence. Chief begins singing Mozart's "The Marriage of Figaro" opera, which prevents Grox's mutated monsters from touching them. Eventually, realizing that the Grox's essence is vulnerable to music, Finn and Jake's friends and allies join in on the singing. Jake is able to amplify the sound of their voices, which allows Finn and Ice King escape from inside GOLB, but Betty decides to stay instead to make a wish. She wishes for Simon to be protected, which causes her to become one with GOLB. The battle ends with a victory and the Grox Leader is sucked through a portal.
The Grox Leader is a manipulative, power-hungry and abusive creature. He enjoys, and is happy to cause, the suffering of others, destroying humans in horrific ways, torturing his enemies and brainwashing them into becoming his subordinates, and even kidnapping innocent children and enslaving them to support his cause, not caring for their mutilation.
At first, the Grox Leader appears as a very professional but still sinister figure, keeping the idea of continuing his job and finishing it in a more professional manner. However, The Grox Leader goes mad with power and forgets about his job and orders, only focusing on destroying Earth, take over it, wipe out the human race, and recrate the Universe in its own image. He also can be quite manipulative as he tricked the failed con artist, T.V., into authorizing a plan to destroy Earth and recreate the Universe in its own image, as he exploits T.V.'s idiocy into approving it.
- His colonies, like every city, have an anthem. It starts with a long static sound, and later someone is singing.
- Despite being the main antagonist, T.V. turned out to be more dangerous and crueler than the Grox Leader.