Sindri then put iron on the hearth, and told Brokkr that, for this next working, they must be especially meticulous, for a mistake would be more costly than with the previous two projects. Loki immediately stung Brokkr’s eyelid, and the blood blocked the dwarf’s eye, preventing him from properly seeing his work. Sindri produced a hammer of unsurpassed quality, which never missed its mark and would boomerang back to its owner after being thrown, but it had one flaw: the handle was short. Sindri lamented that this had almost ruined the piece, which was called Mjollnir (“Lightning”). Nevertheless, sure of the great worth of their three treasures, Sindri and Brokkr made their way to Asgard to claim the wages that were due to them.
–from Norse Mythology for Smart People by Daniel McCoy
Without Loki, there would be no Mjollnir. It was Loki’s mischief, cutting off Sif’s golden hair, that resulted in his traveling to Svartálfaheimr to get the dwarves to make a replacement, along with two other gifts for the gods. And while there, he couldn’t help himself but to challenge other dwarves to make items even more wondrous than the three he already had. We have Loki to thank for Thor’s hammer, Mjollnir.
Without Mjollnir, would Thor have been as powerful? There would be far fewer tales without Mjollnir. One of my favorites wouldn’t have happened at all without Mjollnir because it is the tale of what happened when Thor lost his hammer.
One morning Thor realized Mjollnir was missing. Because all the Aesir relied on Thor and his hammer to protect Asgard, Thor was enraged and searched everywhere, without success.
Freya offered to help by loaning Loki, the shape shifter, her falcon feathers so he could fly to find Mjollnir. Loki took the feathers and flew in search of the hammer. Because Loki was sure one of the giants had stolen Mjollnir, he flew to Jotunheim where he again took his own shape as a god before he approached chief of the giants, Thrym.
Loki asked Thrym if he knew who had taken Mjollner. Thrym proudly admitted he had Thor’s hammer, and he had buried the hammer deep in the earth. He also said he would never return the hammer unless he could have Freya as his bride.
Loki used the falcon feathers and flew back to Asgard to tell Thor and the other gods what he learned. When Loki was finished, Heimdall–not Loki–suggested that Thor should disguise himself as Freya and go to Jotunheim to trick Thrym into giving him back his hammer. Thor objected, saying the other gods would mock him for the rest of his days. Loki pointed out that if Thor did not go to Jotunheim to retrieve Mjollnir, Asgard would be ruled by the giants.
Reluctantly, Thor agreed, and Loki offered to go with him as “Freya’s” servant.
When the two arrived at Thrym’s home, the giant bragged to all those who would hear that he finally had been given a gift worthy of him.
At dinner, Thor ate and drank so much that Thrym became suspicious. Loki quickly responded that the bride had been so looking forward to her arrival that she had not eaten or drunk anything for a week. This pleased Thrym so much that he lifted the veil and faced Thor’s glaring eyes. Thrym turned to Loki and said he had never seen such piercing eyes. Again Loki quickly responded by saying the bride had been so eager to come that she hadn’t slept.
After the ceremony, as was the custom, Thrym presented his bride with his most prized possession, the hammer Mjollnir. Once Thor had the hammer in his hands, he threw off the women’s clothing and struck and killed Thrym. After killing all the rest of the wedding guests, Thor and Loki returned to Asgard.
For more information about Mjollnir, see The Poetic Edda, stanza 51, Vafthruthnismol, The Ballad of Vafthruthnir; stanza 14, Harbarthsljoth, The Poem of Harbarth; stanza 37, Hymiskvitha, The Lay of Hymir; stanzas 57, 59, 61, 63, Lokasenna, Loki’s Wrangling; stanzas 1, 31, Thrymskvitha, The Lay of Thrym;
 Simek, Rudolf. 1993. Dictionary of Northern Mythology. Translated by Angela Hall. p. 219-220.
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