Given Thor's early popularity, it wasn't long before readers wanted to know more about him. This included his upbringing in Asgard. Stan Lee obliged readers with "Tales Of Asgard," short tales that accompanied "The Mighty Thor" in issues of "Journey Into Mystery." For Issue 101, Stan Lee offered "The Invasion of Asgard," one of a series of stories about how young Thor eventually gained his worthiness to hold Odin's Hammer.
When Asgard is threatened with invasion, young Thor grabs his sword and heads off to the front lines. But Odin sends him back, deeming him not yet ready to fight beside him in battle. So Loki offers Thor another way to help out Asgard, by leading him down a secret tunnel.
Thor doesn't hesitate to lend his strength to Asgard's defense.
Little does Thor know that Loki crafted this tunnel, or that he told the evil forces to use his secret tunnel to invade Asgard.
There he meets Ulfrin the dragon, whose breath can transform Thor into a tree.
Thor fights the villains as long as he can, but soon Ulfrin's breath begins transforming him into a tree. Thankfully, Odin hears the noise created by Thor's defense. He leads his army toward the disturbance, where they turn back the invaders. Outside Ulfrin's influence, Thor reverts to his original form.
While Thor believes he's failed Asgard, Odin praises him to his valor. As a reward, he allows Thor to have another go at his hammer. In the past, Thor has failed to lift the hammer, or at most, hauled it a few inches above the floor. This time...
While contemporary issues offer sophisticated storytelling and great artwork, these early stories helped me understand Thor's origin better. In his "Tales Of Asgard" series, Stan Lee fleshes out Thor's childhood, and gives us a better understanding of Asgard's rich heritage and its relationship to Earth. Marvel has no doubt "rebooted" its storytelling universe several times in the past. Thus, Modern readers often find these early stories superfluous. But, as someone whose knowledge of Thor began, for the most part, with the recent movies, these early issues gave me a greater appreciation for the character.
If you'd like to discover for yourself Stan Lee's original conception of Thor, Odin, Loki, Don Blake, Jane Foster, and other marvelous Marvel characters (both mortal and immortal), treat yourself to The God of Thunder, volume 1 in Marvel's epic collection of The Mighty Thor. That is, assuming that you are "worthy" of reading it...