The young Thor was raised with Loki, his step-brother.  Loki had been the son of the Frost Giant leader Laufey, who had been killed by Odin.  Even when they were growing up, Loki was jealous of Thor's powers and popularity.  This jealousy grew into an all-consuming hatred.

When Thor was eight years old, Odin sent him to Nidalvellir, the land of the dwarves.  Thor was to order the dwarves Brokk and Entiri to create three special items for Odin.  One of these items was the Uru hammer called Mjolnir.  Loki somehow sabotaged the creation of the hammer so that its handle was made too short.

Odin enchanted the hammer with many powerful magicks, including one that made it impossible for anyone to lift the hammer unless he or she were truly worthy.  Odin proclaimed that Mjolnir was intended for Thor's use someday, when he had proven himself worthy to wield it.  For the next eight years Thor trained to become a mighty warrior, and he performed many heroic deeds.  Odin then presented Mjolnir to him, and declared him to be the greatest warrior of Asgard.

In the Ninth Century, AD, Thor went to the Earth for the first time.  While on Earth he promoted his worship among the Vikings.  Later on, the Norsemen and Germanic people would also come to worship Thor and the other Asgardians.  While on Earth, Thor encouraged his worshipers to glorify the ways of combat.  One day, Thor discovered that some of his Viking worshipers had killed the defenseless inhabitants of a Christian monastery.

Shocked by the fact that some of his more fanatic worshipers were killing innocents in his name, Thor left Earth and cut himself off from his worshipers.  Over time, the worship of the gods of Asgard died out.

At one point, Odin had plucked out his eye and threw it in the Well of Wisdom.  This eye attained sentience, and grew to a large size.  The eye eventually told Thor many stories about himself and Odin, none of which Thor remembered.  The eye told Thor that he was not the first Thor, the previous one having been killed during the last Ragnarok while fighting the Midgard Serpent.

The eye also told Thor that Odin had once stripped Thor of his godly essence and placed it in two successive mortal forms.  These two incarnations were the two Germanic heroes of legend, Sigmund and his son Siegfried.  In these two mortal guises, Thor played an important part in Odin's schemes to regain the powerful cursed Ring of the Nibelung.  Sigmund was killed by the warrior Hunding, but Thor was then born as Siegfried.

Siegfried was the son of Sigmund and his lover Sieglinde.  Siegfried gained the Ring of the Nibelung after killing the giant Fafnir, who had taken the form of a dragon.  (This Fafnir should not be confused with the dragon Fafnir whom Thor has fought several times over the years.)  Siegfried also gained the Tarn Helm, which enabled its wearer to magically appear as someone else.  During the battle with Fafnir, Siegfried accidentally tasted some of Fafnir's blood, which gave him the ability to understand the speech of animals.  It also gave him the ability to read the minds of those nearby.

Siegfried then fell in love with Brunhilde, a Valkyrie who had been stripped of her godly abilities by Odin when she had disobeyed his commands.  Using the last of her powers, she enchanted Siegfried so that he could be harmed only by attacks from behind.

Siegfried was eventually killed by Hagen, the son of Albreich, the dwarf who had originally created the Ring and placed a curse on it.  Odin then resurrected Siegfried as Thor, but Odin wiped out all memories of his two mortal identities.

As the centuries passed, Thor had many perilous adventures in Asgard.  But over time Odin became concerned with his son's headstrong ways and lack of humility.  After Thor broke a truce by chasing a monster into the land of the Frost Giants, almost causing a war, Odin decided it was time to teach Thor a lesson.

Using the body of a young medical student as a template, Odin created a mortal body for Thor.  This mortal body was given a lame leg, and then Thor, stripped of all his power and memories, was sent to Earth to live in the mortal body.  He appeared on the campus of the New York State College of Medicine, with a false history and background implanted in his mind.  Thus did the life of Donald Blake begin.

Blake applied himself to his studies with great care, and eventually graduated with top honors.  Blake soon gained a reputation as a caring family doctor and a brilliant surgeon.  He opened a private practice in New York City and hired a nurse named Jane Foster.  As time went by, the two began to fall in love.

Odin, knowing that such a love could only end in despair, became worried.  About that time, Odin sensed the arrival of an alien space ship in the Solar System.  The ship was a scout ship for a main invasion fleet of the alien Kronans.  They planned to land on Earth and scout it out for the main fleet.  Odin magically altered the ship's course so that it would land in Norway.

Working quickly, Odin placed a compulsion in Blake's mind causing him to suddenly go to Norway for a vacation.  While walking along the Norwegian coastline, Blake came upon the Kronan ship and he was discovered by the aliens.  Losing his walking cane during his flight from the aliens, Blake took refuge in a cave.  A secret door opened up in the back of the cave, and he found a chamber containing nothing but a gnarled wooden walking cane.  Unknown to Blake, the chamber was where Thor had been born so many centuries earlier.

Exploring, Blake found that the only other way out was blocked by a huge boulder that he could not budge at all.  Frustrated, and scared by the thought of the eventual arrival of the aliens, Blake struck out at the boulder with the wooden cane.

Blake was surrounded by a blazing light, and then he found his body transformed into a powerful form.  The cane had been transformed into a mighty hammer.  Blake instinctively knew that he had become the legendary Thor, even though he still had no memory of his former life.

Thor attacked the Kronans, who fled from his power and strength.  Fearing that the whole planet was inhabited by men like Thor, they called off the invasion.  For several years, Blake acted as the heroic Thor, and his memories slowly returned.  Finally, Odin restored Thor's complete memory and revealed himself.

Thor spent the next few years maintaining his Blake identity and his medical practice.  During this time, Thor saved the Earth many times, fighting many super villains.  Thor helped found the Avengers, a group to which he still belongs.  Later on, he gave up his Blake identity permanently.

The love affair between Thor and Foster continued for many years.  It eventually ended when Jane Foster fell in love with a mortal man, Kevin Kincaid.  Their engagement was cut short when Foster lay dying.  Sif allowed herself to merge with Foster, saving the woman's life.  The two were later separated when Foster was sent to a limbo-realm called the Runestaff of the Possessor.  Thor, Sif, and Kevin Kincaid were later able to rescue Foster, and the two mortals were then married.

Nick Fury, leader of S.H.I.E.L.D., later helped Thor set up a new identity as Sigurd Jarlson, a construction worker.  In this identity, Thor simply pulled back his hair, wore glasses, and dressed like a normal human.

Meanwhile, in a distant galaxy known as the Burning Galaxy by its peaceful inhabitants, Surtur was making his first move toward Ragnarok.  Surtur caused the core of the Burning Galaxy to explode, creating enough energy to re-forge his Sword of Doom.  The disaster destroyed most at the alien empire.  The survivors fled in a fleet of ten thousand starships, hoping to find a new home.

The aliens were all put into suspended animation, except for the one named Beta Ray Bill.  Bill had been converted into a super-cyborg and given a sentient spaceship named Skuttlebutt.  Bill was to guard the fleet on its long journey.  The fleet was being closely followed by a horde of Surtur's demons.

Upon entering the Milky Way Galaxy, the fleet was discovered by a S.H.I.E.L.D. hyperspatial probe.  Nick Fury asked Thor to fly out and investigate.  Beta Ray Bill was awakened by Skuttlebutt when Thor breached the hull of the ship.

The two fought, and during the tight Thor was separated from his hammer, causing him to turn back into Don Blake.  Bill picked up the wooden cane (Mjolnir) and struck a wall of the ship.  Bill was then transformed into an alien version of Thor, holding Mjolnir.  This happened because of Odin's enchantments, designed to bestow the powers of Thor upon anyone worthy enough.  Odin had thought that Thor was the only one worthy enough, but Bill was also worthy.

Skuttlebutt landed on Earth, and Odin then summoned Thor to Asgard. The summons carried Bill to Asgard instead.  Odin then summoned Blake to Asgard and transformed him into Thor.  Thor and Bill made up, but Bill refused to give up Mjolnir; Bill felt that he had taken it in fair combat, and he needed the hammer to protect his people.

Odin ordered a trial by combat, which Bill won.  But Bill felt guilty about taking the hammer that had been made especially for Thor, so he returned it to Thor.  Odin then ordered a new hammer to be made, with the same enchantments and materials as Thor's. Odin gave this new hammer, Storm Breaker, to Bill.

Thor, Beta Ray Bill, and Sif then went to Bill's armada and drove off Surtur's demons.  Since then, Bill has helped protect Earth and Asgard from Surtur and other menaces.

Surtur then joined forces with the renegade Dark Elves.  The Dark Elves and Surtur's demon army attacked Earth, after opening the Ancient Casket of Winters on Earth.  The armies of Asgard and Earth, along with a number of super heroes, drove the invaders back.

Mongoose attacked Thor several times, trying to gain a cell sample from the god of thunder.  Finally, Mongoose kidnapped Eric Masterson and left a trail that led Thor to Wundagore, the High Evolutionary's home.  Thor saved Masterson and joined with the High Evolutionary's New Men in saving Hercules and the High Evolutionary from the mysterious Black Galaxy.  During the recent Evolutionary Wars, Hercules and the High Evolutionary evolved to a higher state and then had disappeared.

Masterson accompanied Thor and helped him free Hercules and the High Evolutionary from Celestials holding them prisoner.  They returned to Earth, while the High Evolutionary turned Wundagore into a spaceship and headed for the Black Galaxy.  Unknown to Thor, a cell sample was obtained from him before Wundagore left.

Hercules, Thor, and Masterson were then viciously attacked by Mongoose using weapons he had stolen from Wundagore.  Mongoose almost killed Thor using a powerful energy beam.  Masterson took a killing blow for Thor, giving Thor and Hercules a chance to defeat Mongoose.  Unfortunately, Masterson was dying from his wounds.

Thor used his hammer to contact Odin, and begged Odin to spare Masterson at any cost.  Odin reluctantly agreed, merging Thor and Masterson together, body and soul.  They now share the same life, much as Blake and Thor had.  Unlike that case, the two were separate beings.

While Thor and Masterson dealt with their new condition, more problems arose.  Masterson's private life suffered from his time away as Thor.  Masterson eventually gave up custody of his son, Kevin, to his ex-wife Marcy.  While Eric thought it was best, his secretary, Susan Austin, disagreed, as she had come to love Eric and Kevin.

Thor's spells of weakness came more often, almost causing his death several times.  Thor asked for help from Doctor Strange, who entered Thor's mind.  Thor accompanied Dr. Strange on this journey.  Inside Thor's mind, they discovered an evil version of Thor, whom the real Thor was able to defeat.  They then discovered that it was actually a portion of Loki's evil essence.

Thor and his friends became plagued by more problems, which Thor soon found were caused by Loki.  Thor and Masterson were briefly separated by a Celestial while they were involved in the birth of a new Celestial in the Black Galaxy.

After this they journeyed to Asgard with the help of Sif.  At the time, Asgard was the scene of a tremendous battle between the fire elemental Surtur and the ice elemental Ymir.  This battle signaled Ragnarok, the end of the universe.

Following Odin's plan, Thor recovered Surtur's sword from the Sea of Eternal Night.  He then confronted the two elementals.  Unfortunately, he was weakened by his separation from Masterson, and was easily stopped by the two creatures.  Masterson willingly merged with Thor again, even though it meant giving up part of his life.

While Ymir and Surfur fought over the sword that would light the Eternal Flame of Destruction, Thor opened a dimensional rift that sucked them both into the Sea of Eternal Night, placing them both in suspended animation forever.

Thor then returned to Earth and found himself once more plagued by Loki and his evil designs.  Loki kidnapped Kevin, Masterson's son, and then stole the Wrecker's Asgardian-given powers.  More powerful than ever before, Loki attacked Thor when he came to rescue Kevin.  After Kevin was taken out of harm's way, Thor beat Loki but could not bring himself to kill his step-brother.

The arrogant Loki surrendered and then shot a magical blast at Kevin and Marcy on the streets below.  The Enchantress, Loki's ally, feared Odin's wrath for her aid to Loki and she mind-controlled Susan Austin to make her take the blast.  Susan saved Marcy and Kevin, but she died from the blast.

The enraged Thor drew out all of Loki's life force with his hammer, destroying the evil god forever.  This broke Odin's sacred rule forbidding Asgardian gods to kill each other.  Contacted by Heimdall, Odin's representative, Thor begged that Masterson be spared and that Earth not be left unprotected.  Heimdall agreed, and then Thor's soul was eternally banished.  The demon lord Mephisto somehow captured Thor's soul and now holds it captive in his realm.

On Earth, Masterson soon discovered that he could now assume Thor's mighty form by striking his cane on a hard surface.  The new Thor apparently still has all of Thor's powers, but only has the experience, mind, and spirit of Eric Masterson.

Another version of Thor exists in 26th-century Earth, in the alternate time line inhabited by the Guardians of the Galaxy.  By this time, the governments of Earth had fallen and the corporations had taken over.  A rebellious cult of workers hoped to someday be free of the tyrannical rule of the corporations.  They tried to find someone who could lift a holy weapon (Mjolnir).  Government forces attacked a cult meeting one night, causing a skeptical cultist, Dargo Kyto, to reach for the hammer.  To his amazement, Dargo found himself transformed into a futuristic version of Thor.

This new Thor destroyed the evil corporation, which was secretly backed by Loki.  During the battle, a troll revealed that the real Thor had been held for centuries in some sort of prison dimension (Loki wanted to make sure that Mjolnir didn't get back to its rightful owner).

Dargo attempted to open a mystical gateway and throw the hammer through, hoping the weapon would find its way back to its owner.  Some time later, the hammer returned to Dargo.  Dargo has since served as the Thor of his time period.