- "Oh, fireballs..."
- —King Reginald Grex
King Reginald Grex is an original character designed by TheAgent41. King Reginald Grex resides in the Goop universe.
King Grex is a diabolical sorcerer who wields a powerful scepter and possesses legions upon legions of loyal Minions to serve his every request. King Reginald Grex lives in the Minion Kingdom, a bleak, wartorn kingdom ruled by him. King Reginald Grex usually resides in Castle Grex, a massive black structure surrounded by a sea of molten lava. He has repeatedly tried to steal the Gooptar Kingdom's stash of Magic Opals and take over the planet Gooptonia, but he is always defeated by Goop and his friends.
King Grex's early history is vastly unknown. He only really first came to the attention of the Gooptar Kingdom when he enacted an assault on the castle of the kingdom's benevolent ruler, Princess Blossom. Attacking the Gooptar Kingdom's capital city with his futuristic airships, King Grex, along with his lackeys Moki and Shelldon, spirited the princess away to his castle, along with the Gooptar Kingdom's collection of Magic Opals, ancient artifacts that contain the life force of the planet. He was soon defeated by Goop, who stormed the castle, fought Grex, and rescued the princess. Meanwhile, Grex was accidentally devoured by the lava dragon Magmass, who was shot out of the sky by Bing and Draclo. Grex is later seen rising from the grave and ordering Moki and Shelldon to build a robotic version of his body for his spirit to inhabit.
King Grex is a 5-foot yellow, dinosaur-like creature. He has 4 clawed fingers on each hand and 3 clawed toes on each foot. He has a long tail tipped with a "brush" of spikes and he has another "brush" of spikes on his head. He usually wears a large golden crown with 5 spikes on it, orbs that tip each spike, and a red jewel. He's also seen carrying a golden scepter with a large red jewel encrusted within it. He also wears a black cape and sports a long gray fu manchu mustache.
After his death, his spirit inhabits a silver robot version of himself with glowing yellow eyes, the same color as his ghost.
King Grex is an extreme megalomaniac, a creature who only wishes to take over the Gooptar Kingdom and the planet Gooptonia. He is constantly shown to be selfish, self-centered, and very proud of himself. Despite not really being a king, he insists on claiming his royal lineage. He is a horrible and abusive boss to his Minions, beating them whenever they inevitably screw up. King Grex could easily be described as a large ham, constantly shouting at the top of his lungs in anger in his trademark British accent. He is extremely boastful and shallow, claiming to be the most powerful being in the world. He is also extremely persistent, never giving up on his nefarious quest.
- Political Power: King Grex is the leader of the Minion army, granting him power of a vast army of henchman ready to risk their lives for him.
- Magic Scepter: King Grex possesses a magical scepter of unknown origin. Said scepter grants King Grex the ability to cast a variety of magical spells, as well as shape-shift and move objects from a great distance away.
- Shape-shifting: King Grex is capable of changing his physical form through magical means, taking on various forms such as a giant muscle-bound version of himself or a massive snake.
- Magic Rockets: One of King Grex's favorite spells, this spell fires a series of energy spheres from the tip of the scepter. These spheres home in on whomever Grex is targeting, making them very dangerous and very deadly.
- Moki the Grumbly: Abused lackey
- Shelldon the Torto: Abused lackey
- Frogrump: Frequent employee
- Crocrump: Frequent employee
- Goop the Gooptar: Arch-enemy
- Bing the Gooptar: Enemy
- Draclo the Dragon: Enemy
- Tawnya the Gooptar: Enemy
- Princess Blossom the Gooptar: Enemy and frequent victim of kidnappings
- King Grex's name is derived from the Latin rex, meaning "king". Then, the letter "G", the first letter of Goop's name, was added to the beginning.
- Grex's ideal voice actor would be TheAgent41.
- Grex will be the main antagonist of a video game series developed by TheAgent41.