Thanos Feared an Attack From Odin and He Might Have Been Planning One. However, it's possible that Odin kept his kids in the dark because he was preparing to take on Thanos all along.
Odin in the MCU's universe is stronger than Thanos. He defeated, or could defeat, many, many enemies who could possibly defeat Thanos. Like Surtur. Pre-Awakened Thor was weaker than Odin.
He simply wanted him dead at all costs because he was his biggest threat. As per the user, the director of Avengers confirmed that Thanos was most scared of Iron Man. “Not because of his strength, not because of his power, not because of his power, but because of his suit,” he added.
Odin was killed off out of necessity, so that the most powerful single entity was not a good guy. Was Thanos aware of Odin's existence before their encounter in Asgard during Avengers: Infinity War? Yes, Thanos knew about Odin.
As for the reason Odin didn't strike Thanos first, his last few years were plagued by tragedy. After an attack by the Dark Elves led to the murder of his wife, Frigga, he was placed under Loki's spell and sent to Earth, where he would spend his final days.
But the one being Thanos hates more than anyone is the Merc With A Mouth himself, Deadpool – a rivalry that MCU fans are likely going to miss. While many fans may not expect this rivalry, Thanos and Deadpool have been at odds for quite some time.
If he was relatively calm Odin would probably engage the Hulk physically to underline the difference in power between them. Odin would crush hulk! Odin is the most powerful being in the nine realms outside of cosmic entities.
While Thanos is an Eternal and has the standard powers of super-strength, agility, regeneration, immortality, and more, Adam Warlock takes the upper hand. He can be killed, but he resurrects to be stronger every time.
So while Zeus' best feat is defeating a mountain-sized monster, Odin's best feat is defeating a monster as big as nine worlds. Odin outclasses Zeus in intelligence, versatility, strength, and weapons. Zeus simply can't compete. The winner is Odin, All-Father of the Æsir.
During the three years, Odin became weary of Kratos' presence in Midgard, fearing that the Ghost of Sparta could challenge his control over the nine realms or ruin his plans.
A significant part of Thor's trauma stems from his failure to kill Thanos in Avengers: Infinity War, leading to the Mad Titan's devastating Snap. Thor had Thanos comfortably beaten, yet did not strike a blow at his head, instead curiously deciding to sink Stormbreaker into the great Titan's chest.
Odin stands a good chance at defeating a moderately-fed Galactus. Odin has been stated to be equal to a moderately-fed Galactus. Though Galan did withstand a powerful headbutt from Odin. The Devourer had just consumed one planet before that.
In "Avengers: Infinity War," Loki fears Thanos due to their past encounters and the threat Thanos poses to him and those he cares about, particularly his brother Thor. Loki's previous experiences with Thanos likely left him aware of Thanos's power and ruthlessness, contributing to his fear of the Titan.
Loki, essentially, has a lot to fear from the inherent classism of the godly society he inhabits. Loki screws up often — but so do other gods from more “acceptable” backgrounds. Loki is held accountable for his mistakes, often painfully; they are not, or they get a slap on the wrist by comparison.
Prior to his appearance in Quantumania, though, Majors made his MCU debut in the Season 1 finale of Loki, playing one (of many) variants of his villain Kang the Conqueror named He Who Remains.
He also ensures that some of the technology Kang will need gets invented (Tony's time travel machine). As he gamed this particular fight over and over, maybe more than 15 million times, He Who Remains chose this specific set of events. He caused Heimdall, Loki, Gamora, Black Widow, and Iron Man to die.
Not long after, he attempted to cure Thor after the Thunder God had lost his sanity, but the attempt was in vain. He transported Thor back to Asgard where Odin took this as an act of war and fought an extremely destructive battle with Thanos.
Odin revealed that he wanted to gain a permanent peace between Asgard and Jotunheim by having Loki rule the world of the Frost Giants. Loki was disgusted by his own parentage and claimed that Odin could have never loved him the same way he loved Thor and would have never given him the throne.
