What Is Ego's Plan?
The core of Ego's plan is "expansion". His quest to find life was originally gratifying, confirming his suspicions. However, being a Celestial and self-professed god, over time he gradually began to see the flaws of the species he discovered and realized that to truly save the galaxy he would have to become it. His solution was to continue what he's achieved with his planet and slowly take over more and more worlds, growing and spreading throughout the universe. He planted pods on thousands of worlds hoping to extend his reach.
However, even with his planet-creating ability he wasn't solely powerful enough to enact such a plan - he needed a partner with Celestial DNA who was capable of helping wield his life force, so set about creating such a being himself; he traveled around the galaxy to the various species he discovered and mated with hundreds of different aliens. Once the offspring was born, he would then send Yondu, who was breaking the Ravager code to do so but received a sizable recompense, to go collect them when they were old enough.
When he had his children, he'd test them for any Celestial DNA and the ability to tap into his power. If they showed no signs, then he'd kill them and bury their bones underneath his utopian planet's surface. This is pretty much how things went... until Star-Lord.
Where Does Peter Quill Fit In?
Peter Quill, Ego's human son, was already different to the many other children due to the feelings the Celestial felt for Meredith Quill; he visited her on Earth three times and feared he'd ditch his conquest plans and never leave the planet again if he visited a fourth. His maniacal thoughts prevailed, though - love didn't stop him from killing Meredith, planting the brain tumor that killed her at the start of the original Guardians (it's not explicitly stated, but is likely he did a similar thing to his many other mates).
Ego sent Yondu to collect Quill like the many previous experiments, but knowing his fate and seeing something in the Terran, the Ravager chose to raise the boy instead of delivering him to his tyrannical father. He used the excuse that Peter's size made him "easier for thieving", something both characters repeat at various points in Vol. 2 (and is referenced by Baby Groot's part in the final battle), and kept the child in check with the threat of cannibalism. When Peter - now assuming the role of Star-Lord - saved the galaxy at the end of the first film, Yondu felt his work was done (despite the betrayal it involved).
However, Peter being able to hold the Power Stone by himself when defeating Ronan (something Nova Prime commented on at the original's climax) brought him to the attention of the wider galactic community. When Ego heard of a human with such power, he knew instinctively it had to be his son. He and Mantis set about looking for Quill and, after a few months of searching, found him after the misunderstanding on Sovereign.
The Celestial plays on the innate emotion of Quill meeting his estranged father, trying to be everything Peter ever wanted and more - Quill learns that he is immortal and in the proximity of the planet able to use psionic powers to build anything, naturally leading to a game of catch - before carefully revealing his true plan; Ego first tries to get Peter onboard willingly, but when it's clear Quill has too much compassion he instead decides to use him essentially as a battery.
The whole thing is eventually brought down by the Guardians working together and Star-Lord making the conscious decision to forfeit his immortality for the good of the universe, an explicit contrast to Ego's ethos.
- Avengers: Infinity War / The Avengers 3 (2018) release date: Apr 27, 2018
- Captain Marvel (2019) release date: Mar 08, 2019
- The Avengers 4 / Avengers: Endgame (2019) release date: Apr 26, 2019
- Ant-Man & The Wasp (2018) release date: Jul 06, 2018
- Thor: Ragnarok (2017) release date: Nov 03, 2017
- Guardians of the Galaxy Vol. 2 (2017) release date: May 05, 2017
- Spider-Man: Homecoming (2017) release date: Jul 07, 2017
- Black Panther (2018) release date: Feb 16, 2018