Getting bored with his 10 million year rule over Asgard's virtually unbeatable military, he seeks to show his power where he is needed, hence, he picks a planet where this much suffering and the beings are in need of a leader: Earth.
As Thor travels around Earth(21st century), he notices that they are primitive, and many aspects are of their society are conflicting yet go together in harmony-religion and science, beauty and ugliness, peace and war-and for this insight into the human psyche Thor decides to stay and claim himself as Earth's protector.
Flying around Earth, mjolnir detects a unique energy signature entering Earth's atmosphere-graviton manipulation. looking up into the sky, Thor realizes the Kronans have come to Earth! "Odin's beard!" Thor comments, as the Kronan ship lands. Believing they come for peace, Thor puts his hammer at his waist and prepares to greet the aliens. But, unbeknowst to him, the Kronans have another goal in mind-world domination.
As Thor holds his hand out, he's shot and a carbodonium cable(indestructible cable that only the surface of the sun can destroy) wraps around Thor, releasing poison gas. "Hello there, Earthling." the Kronan says. "Before my species conquers this planet, I must be figure the anatomy of this planet's species. This planet, that's as green as the Hulk and third from its sun."
As Thor frees himself from the cables, one of the Kronans notices this, and pulls out an energy blaster, Thor, thinking he can withstand the blast, doesn't know it's actually an anti-force canon, that which negates and knocks out any force-or any one-in its path. With one blast, Thor is rendered unconscious.
"Now we have a specimen," the leader of the Kronans said, as he stands tall wearing a black armored vest with a energy canon(specifically anti matter ray gun) at his waist. "Take him to the ship, and begin testing."
The Kronans take Thor onto their ship. And begin experimentation. Thor, looking over his shoulder, notices a picture of a female Kronan(which is unusual, because Thor knows that female kronans are more rare in the Kronan species than is a human that's immune to all diseases). Thor asks "who's that?' the leader of the Kronans replies, "Shut up! You mind your own business, human with a hammer!" With that last word, Thor becomes impatient and decides to break out of the indestructible chains that the Kronans put around Thor. One of the Kronans, trying to attack Thor, tries to lifts Thor's hammer but to no avail. "Why can't I lift this hammer?" The kronan says. Thor replies "an enchantment, a mystical energy surrounding the hammer, means noone can lift the hammer except for me!" The leader of the Kronans realize that Thor has something more than a mere hammer, he has a mystically enchanted weapon. The leader of the Kronans tells the Kronans to back off and let Thor return to Earth. The Kronans ask, "why Korgan?"(leader of the Kronans) Korgan replies "Because we are no match for this human! That's why!"
Thor, believing to have won, flies off the warship hovering in orbit around Earth and flies back to Earth. Unknown to Thor, the entire fight was captured on the Kronan's log(video), and via reverse engineering, Korgan created a suit that is empowered by the same mystical energies which enchant Thor's hammer(residual energy is left whenever any form of energy is dissipated into the surrounding environment, although its remmants last only for a few minutes).
With their new weapon, the Kronans plan to take Thor's hammer, and figure out all of it's abilities and attempt mass produce it and arm their people with an unstoppable weapon.