Ego is a major antagonist of the Marvel Cinematic Universe, as a major antagonist of Phase Three. He is one of the overarching antagonists of Guardians of the Galaxy, the main antagonist of Guardians of the Galaxy: Vol. 2 and a posthumous antagonist of Avengers Infinity War.
He is portrayed by Kurt Russell
Guardians of the Galaxy Vol. 2
In the opening of the film, during the past, Ego is shown with Meredith Quill on Earth during the 1980s. Ego then takes Meredith behind a Dairy Queen and shows her a beautiful small blue flower, and pridefully claims that soon it will be grown all across the universe. Meredith states that she doesn't understand what he is saying, but loves the way he is saying it before continuing to make out with him.
In the present, Ego rescues the Guardians from Ayesha by obliterating all the drone ships chasing them, although only Rocket notices him. After the Guardians crash land on a nearby planet, Ego and his servant Mantis descend onto the planet and Ego introduces himself as Star-Lord's father. Star-Lord and his father then get to know each other and Ego offers to let his son and his friends come to his planet, and, while Star-Lord has doubt about his true intentions and that he may not be his true father, Gamora assures him that there is a good chance that Ego is his true father and that he shouldn't let this opportunity slide. With that, Star-Lord, Gamora and Drax depart with Ego and Mantis, while Rocket and Groot stay behind with the captured Nebula. On the ship, Mantis uses her powers to help Ego sleep.
On his world, Ego shows his son, Drax and Gamora the beauty of his planet. Ego then explains his origin; Millions of years ago, he was a small, speck like being that developed thought and learned to control matter, eventually building himself the planet. Ego then searched the cosmos for other forms of life, eventually finding life and falling in love with and impregnating Meredith Quill on Earth. After he heard about how Meredith had contracted brain cancer and was dying, he hired Yondu Udonta to retrieve his son from Earth and deliver him, although Yondu didn't follow his orders and instead kept Quill around because he could fit inside small spaces and Ego has been searching for him ever since.
Peter Quill then angrily asks to know why Ego abandoned his mother during her time of need and he states that, if his planet isn't under his constant attention, it will dissipate. Ego then tells his son that he does truly care for him and wants to be the father that he never got to be. Ego then shows Peter how to access his Celestial powers, teaching him how to create and playing catch with him, something Peter was upset over never having done. Meanwhile, Mantis, while bonding with Drax, attempts to tell him something about Ego's planet, but decides not to when Gamora unintentionally interrupts them. While exploring the planet, Mantis states that there are no other people on the planet because "a dog doesn't let fleas onto it's back". When questioned by Gamora over what she was about to say, Mantis hesitates and claims she wasn't going to say anything. Because of this, Gamora becomes concerned over what Ego's intentions are and ends up at an impasse with Star-Lord, who completely trusts his father and wants to bond with him.
After Gamora leaves and tries to contact Rocket (ending up in a fight with Nebula), Ego continues to teach Peter about his abilities, stating that, as long as the Planet's core is intact, the both of them are immortal. Ego then prepares to show Star-Lord the purpose of their existence and expands on his origin, giving his son the ability to see the entire universe at once, all of which is witnessed by Mantis, who heads off to warn Drax of what Ego has planned.
Ego explains that, when he found other life in the universe, he was disappointed at what he found and decided that the purpose of all life in the universe was to become him, and that the "flowers" he had planted were actually all extensions of himself that he planted in thousands of different worlds. Ego soon realized that even a single Celestial wouldn't have the power to activate all the extensions at once, however, two would, and then began breeding with thousands of different alien species in order to find the one who's genetics would line up with his own and create a new Celestial, and would then have Yondu retrieve the child he created for him, however, every single child conceived was a failure that Ego soon killed (the skeletal remains of which were all discovered by Gamora and Nebula). Ego then stated that the one thing he did not expect was actually falling in love with Meredith Quill, and knowing that his love would get in the way of his goals, he decided to get rid of her once Peter was born, stating that "It broke my heart when I had to put that tumor in her head." Realizing Ego's horrifying goals and the fact that he was responsible for his mother's death, Star-Lord angrily began shooting him and blowing his form to pieces, although he easily regenerated them. Knowing that his son would never go along with his plans, Ego uses his powers to posses his son and starts activating the extensions. Before his plans could go any further, Yondu and Rocket crash their ship directly on top of Ego, temporarily stunning him while the team freed Star-Lord and got away. After escaping, Yondu wished to leave the planet as soon as possible, however, Star-Lord stated that his father was too dangerous to be left alive and has Yondu fly down to the planet's core, as it is the source of all Ego's power and life.
The team tries to burn a hole in the core's protective layer, however, Ayesha and her Sovereign drones arrive and try to kill the Guardians again, at the same time, Ego manages to find them and uses his energy tentacles to try and kill them. Drax then manages to convince Mantis to use her powers to make Ego fall asleep, temporarily putting him out of the fight, although Mantis eventually ends up being knocked out during the chaos, allowing Ego to continue trying to destroy the Guardians. Ego's physical form then surfaces underground and berates Star-Lord for trying to stop him, eventually managing to have all the Guardians at his mercy, starting to crush Rocket, Gamora, Groot, Nebula and Yondu to death, drowning Drax in the sand and possessing Star-Lord yet again and beginning to re-spread his extensions, telling his son that there is nothing worth fighting for except power.
After getting some inspirational words from Yondu, Star-Lord tells his father that he shouldn't have tried to hurt his friends or his mother, before harnessing his own Celestial powers, breaking free from his father's control. Star-Lord then begins to mercilessly pummel his father into submission whilst simultaneously saving his friends and stopping the spread of the extensions. As Star-Lord and his father fight, Groot delivers Rocket's bomb to the center of the planet and arms it, allowing the team five minutes to escape, with Rocket regretfully having to leave Star-Lord behind in order to not risk the lives of his other friends. Exhausted due to having fought each other at their full power, Star-Lord, too tired to use his powers, continues beating and holding down Ego in order to prevent him from getting to the core. Ego then shouts at Peter, telling him that, if he allows the core to be destroyed, he'll be normal, although Peter simply asks him what the problem with being normal is, causing Ego to scream in agony as the bomb goes off and destroys the core, turning him into dust.