MCU completely rewrites the origin and characteristics of MODOK
Ant-Man and the Wasp: Quantumania introduces Marvel Comics villain MODOK to the MCU with a very different spin on the character and background.

Warning! This article contains spoilers for Ant-Man and the Wasp: Quantumania.
Ant-Man and the Wasp: Quantumania introduces MODOK to the Marvel Cinematic Universe, making some major changes to the character's comic book origins in the process. As we all know since the MCU started with Iron Man in 2008, Marvel Studios isn't afraid to take creative liberties with their comic book characters. Interestingly, this trend is mostly reflected in the MCU's roster of different villains.
From Zemo and the Mandarin -- from Iron Man 3 instead of Shang-Chi and The Legend of the Ten Rings -- to characters like Aldrich Killian, the MCU often doesn't shy away from making changes to comic book villains as it sees fit. This is followed by the first film of Phase 5, Ant-Man and the Wasp: Quantum Fever, and introduces MODOK into the universe alongside powerful MCU variant Kang the Conqueror. That being said, here's an explanation of every change Quantumania has made to MODOK's character, and how he fits into the sprawling MCU.
Which Character Is MODOK In Marvel Comics (Not Darren Cross)

The biggest change in MODOK is undoubtedly the man under the armor. In Ant-Man and the Wasp: Quantumania, MODOK is revealed as Darren Cross aka Yellowjacket The first Ant-Man movie. In the comics, however, the most famous version of MODOK is that of a man named George Tarleton. In the Marvel Comics, Tarleton was a technician for a criminal organization called AIM, which appeared in the MCU's Iron Man 3.
Obviously, the MCU changes are huge. Often, the MCU changes its villains to better fit the stories they're used to, though many elements remain the same. However, in Ant-Man and the Wasp: Quantum Fever, MODOK's original comic character has been completely erased. Marvel Studios opted to replace George Tarleton with Darren Cross to maintain continuity between the Ant-Man films.
MODOK's Origin In Marvel Comics Explained

Another difference between the MODOK comic book version and the MCU is his origin. After enlisting as a technician at AIM, Tarleton was forced to become a MODOC, a psychic organism designed for computing, so that the company could research something called the Cosmic Cube. Therefore, George's existence was altered to create MODOC. This quickly went wrong for AIM, and MODOC became MODOK, the psychic organism designed to kill.
Marvel Comics supervillain MODOK is thus created and revolted His creator grew his ambitions because of his newfound superior intelligence. MODOK killed everyone at AIM and took control of the company for himself. This has put him at odds with many Marvel heroes over the years, from Captain America and the Hulk to anti-heroes like Namor, as one of Marvel's core supervillains.
Why MODOK Has Such A Giant Head

One of the central issues surrounding MODOK in the comics and MCU stems from his grotesque appearance. In the comics, MODOK has a huge head and tiny hands and feet, and uses a floating chair called the "Doom Chair" as a means of transportation. The reason for this comes from the original intention of MODOK. When AIM created MODOC, George Tarleton's increased intelligence and brain size caused his skull to grow larger, creating giant creatures.
However, the answer to why MODOK's head is so large in the MCU is slightly different given the significant changes made to the character. The character's strange appearance is tied to the character's fate at the end of the first Ant-Man, thanks to writer Jeff Lavness's Darren Cross MCU MODOK for Ant-Man and the Wasp: Quantum of Fever. Scott damaged Darren's Yellowjacket suit, which drastically alters his body, with Pym particles creating the massive head and small appendages seen in Quantumania.
Why & How Marvel Made Darren Cross MODOK In The MCU

All of this begs the question of why Marvel Studios chose to make Darren Cross the MCU's version of MODOK. The answer simply stems from creating continuity between the Ant-Man films. If Marvel Studios had used George Tarleton's version of MODOK in the film, they would have had to write the character's backstory, which the film's 124-minute running time probably wouldn't allow. Instead, using Yellowjacket from Cross/Marvel Comics as a character to become MODOK means no backstory is needed, as it's already been told in Ant-Man, and Quantumania can continue that story.
Also, using Scott's nemesis as an antagonist in this film helps to build up even more stakes. It allowed MODOK to form a personal connection with the heroes of the film, from Hank and Hope to Scott and Cassie. All of this makes Cross as MODOK a lot of sense in terms of the broader MCU story, allowing Ant-Man and the Wasp: Quantumania to include iconic villains in ways that befit the cinematic universe, albeit mostly Change the manga that inspired it.
How MODOK's MCU Powers Compare To Marvel Comics

For the most part, MODOK's MCU functions remain similar to the Marvel Comics version, although there are some changes. Instead of being placed in a doomsday chair like in the comics, MODOK was transformed by Kang's Quantum Realm futuristic technology to create a suit of mechanical armor. Although not the same as the chair, this armor allows the MODOK to exhibit similar powers, such as weapons such as missile launchers and laser launchers.
Some differences in MODOK capabilities in MCUs stem from different origins. The manga version of MODOK is very smart, which often allows him to figure out his own way out of situations. The MCU version is only as smart as Cross before it became MODOK, though. The comic version of MODOK also has psychic abilities that the "Ant-Man and the Wasp: Quantum Fever" version does not have.
The MCU's MODOK Is Less Of A Supervillain Than The Comics

Darren Cross/Yellowjacket Another change brought about by the MCU's MODOK has to do with his evil ways. In the comics, Murdoch is more of a supervillain, often running afoul of the various Avengers due to his nefarious ambitions. In the MCU, though, the character is portrayed more as A follower who works for Kang in the Quantum Realm. MODOK is used as Kang's "hunter", blindly loyal to Kang because his technology saved his life.
How MODOK's MCU Death Compares To The Comics

At the end of Ant-Man and the Wasp: Quantum of Madness, Darren Cross' brief career as a supervillain ended when Mordoc was killed. Despite being the villain for most of the film, MODOK changes his mind at the end of the film after talking to Quantumania's Cassie Lang. Deciding to change his ways, MODOK tried to attack Kang but to no avail, the Conqueror subdued him using his tech-based powers. This seriously injured MODOK and he died soon after.
This death is different from George Tarleton's death as Murdoch in the Marvel Comics. In the comic storyline, AIM wishes to distance itself from MODOK and his evil ways, and hires the Viper Society to assassinate him. The group succeeds, with supervillain Death Adder delivering the final blow. While MODOK is eventually resurrected, this version of his death is very different from the version shown in Ant-Man and the Wasp: Quantum of Fury, marking the latest in a long list of differences between the MCU's MODOK and the comics Inspired his book counterpart.