|First Episode||Pinstripes & Poltergeists|
|Voiced By||Christopher McCulloch|
|Profession||Super Villian/ Lawyer|
|Alliances|| The Guild of Calamitous Intent|
Monstroso was an influential supervillain and lawyer of the Mammoth Corporation.
Monstroso was a 13 foot tall super-villain who served as the attorney for the members of The Council of 13. He had many affiliations and was targeted by both the O.S.I. and S.P.H.I.N.X.. Monstroso had a personal army of henchmen, the Associates, who wear red hoods with an embroidered 'M' on the front, some of which were former Monarch henchmen who joined up after the Monarch went to prison. Monstroso was reputable for his penchant to double-cross and offering his cigars to his clients. He had a romantic relationship with Molotov Cocktease which made Brock Samson extremely jealous. He also had previously made deals with The Investors, whom worked for by proxy of his membership with the Guild of Calamitous Intent.
In "Pinstripes & Poltergeists" Monstroso tried to double cross the Monarch by seizing his arch-enemy's (Rusty Venture) property and his own through legal means. He was prevented by Henchman 21 and Brock Samson, and exposing Monstroso's plans.
After his ordeal with Henchman 21 and Brock Samson, Monstroso was dying of heart failure and made a deal The Investors in requiring a heart transplant in exchange to rescind his life sentence. The Investors kidnapped Billy Quizboy to operate Monstroso's surgery by replacing his failing heart with King Gorilla's, and Monstroso return Billy's favor by forging his credentials that officially recognize him as a doctor. After the surgery, Monstroso was captured by S.P.H.I.N.X.. However, Monstroso escaped with the help of his lover, Molotov Cocktease.
In the episode "O.S.I. Love You" he along with Molotov was recaptured by O.S.I. and brought to the O.S.I.'s hover carrier. Monstroso was interrogated by Brock and freely tells him everything he knows about the Guild, as he claims to be "as good as dead" anyway since the Guild would be coming for him. When Molotov escaped and causing O.S.I. personnel to be distracted, Monstroso's fears came true when The Investors appear before him and killed him by phasing out of the hover carrier and dropped him to his death. Brock was the last person who saw Monstroso, but he did not see The Investors. The O.S.I. listed Monstroso as officially "Missing".
- Trial of the Monarch (mentioned)
- What Color is Your Cleansuit? (fake body)
- Monstroso shares a number of similarities with Marvel Comics villain, The Kingpin, including his monstrous size and being a businessman running a criminal empire. He also shares some traits with Anton LaVey, founder of the Church of Satan, including his facial hair, devil hood, and general devil motif.