Another interesting theory posits that God and Saitama are, actually, the same person, due to the hero's recently revealed ability to manipulate spacetime and alter timelines.
Saitama wants infinite power, but at the same time he wants an opponent who can challenge him. Unfortunately for him he can't have both. Eventually he will either have to weaken himself or encounter another God with unlimited power. TL;DR: Saitama is a God, but he doesn't know it.
The character referred to as “God” in One-Punch man is an otherworldly being that appears to grant people power but at great cost. The well-drawn character has made its appearance in different chapters in the manga, puzzling fans on the true nature & goal of this being.
God finally appeared to Saitama, the S-Class hero Flashy Flash and the monster Oculette, when they touched a strange, cube-shaped object, and were able to hear God's voice in their heads. He offered them to make a "fervent wish", to see if they were "worthy vessels to bestow my power upon".
Saitama takes on God in One-Punch Man: The Fight of Gods, a passion project for one fan artist. In an effort to save the universe, Saitama punches God in the face in the non-canonical One-Punch Man: The Fight of Gods, a fan-made comic based on the popular anime, manga and webcomic.
With his ability to capture enemies into Imprisonment balls and his card attacks, he proved the might of his power and emerged victorious against many other gods during the exhibition match. Saitama could prove to be a formidable opponent, but sadly, it is likely he will not be able to conquer the God of Universe 11.
He is quicker, stronger, and more resilient than anyone else. Considering God is interested in bestowing their power on strong individuals, there is no better candidate than Saitama. If the two ever cross paths again, God will likely offer Saitama the opportunity to become even stronger.
Although he tells everyone he got his incredible power through mere physical training, no one believes him at all. According to Saitama, after a year and half of 100 daily push-ups, sit-ups, and squats, plus 10km daily running, he had achieved some level of superhuman strength.
The only event that came close to becoming a God-level Disaster Threat was the meteor in the first season, which Saitama managed to stop easily. Otherwise, for now, it seems like the only God-level threat that the universe might face is from God himself, who has made himself known numerous times in the manga.
Genus, Saitama is no mere superhuman, but actually a monster. He theorized that there exists an artificial limit to which humans can grow stronger, dubbing it the “Limiter.” Put in place by God himself, the very existence of the barrier prevents humans from entering “the realm where we lose all purpose and reason.”
A leading fan theory regarding the source of Saitama and most characters' strengths is that they trained and dedicated themselves to an inhuman level. The result of their high-level dedication is supernormal strength that is unusual for a human. In fact, many heroes in One-Punch Man can be linked to this theory.
Comparatively, Goku's physical feats and abilities are far stronger than Saitama's. He's obliterated the walls of an alternate dimension and shook a universe by just arriving in it.
Personality. God's motives are extremely enigmatic, but what seems to be apparent is that God harbors a strong hatred for humanity and desires nothing else but their extinction. God's reasonings for bestowing power upon others is unclear but it seems to usually be those that follow its beliefs.
A Saitama hailing from an alternate dimension, this wicked and evil counterpart of Saitama seeks only destruction, devastation, and causing chaos, his obsession with finding an opponent strong enough to challenge him consuming him entirely, causing him to forsake his status as a hero and walk the path of pure evil, ...
That is, God's height is approximately 84% of the Moon's diameter. If the Moon in the One Punch Man universe has the same dimension as the Moon in our universe, that is, considering it a perfect sphere 3,474.8 km in diameter, we have that the height of God is approximately 2,921.4 km.
That being said, Saitama hasn't used his full power in any of the fights in One Punch Man. However, fans expect him to go all out at some point in the story and are eagerly waiting for the character or the entity that will push Saitama to his absolute limits.
Thus, it is safe to say that Limit-breaker Saitama cannot beat Goku in his Ultra Instinct form. It is far too powerful a transformation to contend with. Even if Bald Cape lands his Zero Punch, Goku has been seen multiple times being more than capable of taking a hit.
Saitama is unable to fly, or to use energy-based attacks as Goku can. Also, the Saiyan possesses greater combat experience, having constantly trained and battled with the most powerful warriors in the universe, while Saitama is unable to find anyone that can truly challenge him.
But, upon reaching the current timeline, Saitama lost his ability to time travel, an ability that only Genos remembers now because of the replacement of his core. Thus, this is how the Caped Baldy became weaker in chapter 169 of One Punch Man.
Being a supernatural deity, Rimuru is immune to any kind of physical attack, so Saitama's punches are a no-go. Moreover, destroying his physical body won't kill him unless his core is destroyed, that is, his soul. Until Saitama uses some special magic spell, he cannot defeat Rimuru.
This reference was then overshadowed by the incredibly epic battle between Saitama and Garou, but the manga has now confirmed that, in fact, God is aware of Saitama's existence and is attracted to him for unknown reasons.
The mere comparison of strength between the two characters is crazy. Goku is an extraterrestrial being who has to lose a fight in order to get stronger. Saitama is a man that can defeat any foe with a single punch. If the two of them were to face off in a one-on-one battle, Saitama would easily win.