Mjolnir is the hammer that is wielded by Thor. Odin ordered the Dwarves of Nidavellir to forge Mjolnir. The dwarves Eitri, Brokk and Buri used heat from a star to get the forge hot enough to manipulate Uru. The star exploded, destroying Midgard. Odin couldn’t wield it so he cast an enchantment on it to prevent others from doing so. Odin gave the hammer to Thor after he successfully past several trials.
Mjolnir is a powerful “nigh-invulnerable Asgardian metal.” Odin placed additional enchantments on it making it almost indestructible. Almost nothing can survive a blow from Mjolnir. The most well known enchantment is the “worthiness enchantment.” Those who are deemed “worthy” can lift the hammer gaining the ability to manipulate the weather, fly, energy projection, barriers, energy sensing, energy absorption, teleportation, and matter manipulation.
The reason I love Mjolnir is pretty clear, it’s cool. However, I have always personally loved mythology and seeing it in Marvel always gave me joy. Finally, I love a weapon that seems to have a mind of it’s own.