Since being introduced in the Marvel Universe in Journey into Mystery #83, by Stan Lee, Jack Kirby and Larry Lieber, Thor has wielded his most distinctive weapon: the enchanted hammer Mjolnir. Only capable of being utilized by the most worthy of souls, it's become a consistent presence in the Marvel Universe.
But sometimes, Thor ends up not being capable of wielding the hammer. In those times, Marvel has given Thor a different weapon to go into battle with. That's where the axe Jarnbjorn comes in. Created by Jason Aaron and Esad Ribic in Thor: God of Thunder #1, it's one of the oldest weapons Thor possesses and has become his go-to blade in desperate times. Here's the history of that axe across the Marvel Universe and how it even appeared (sort of) in the Marvel Cinematic Universe.
WHY DOES THOR USE AN AXE?
Jarnbjorn was introduced as the weapon Thor primarily used before he was worthy enough to wield Mjolnir. This younger version of Thor was more haughty and blood thirsty and hadn't yet learned the restraint that the future king of Asgard would need. Taking the axe with him when he came to Earth, he used it in his battles against theFrost Giants that targeted the vikings of the 9th century.
This was the weapon the young Thor needed to use when Gorr the God-Butcher targeted him, and it was even what he used when he fought alongside two future forms of himself (the modern incarnation of Thor and the ancient King Thor) in the "God Bomb" story line.
CAN THOR KILL A CELESTIAL?
The axe ended up playing a more central role for Thor in the build-up to Secret Wars. It was revealed that during an 11th century battle with frequent X-Men villain Apocalypse, Thor blessed the axe with his own godly blood so that it could be used to crack through Celestial empowerment. This came back to bite the heroes of Earth however, when the axe was eventually used to frame Thor for the murder of a Celestial in Uncanny Avengers. This resulted in the (temporary) destruction of Earth, although this was reversed by the conclusion on Uncanny Avengers.
Thor would soon need the axe again however. After the events of Original Sin left Thor unworthy to wield Mjolnir, he started using Jarnbjorn again. It served as his primary weapon during his period as the Unworthy Thor, while Jane Foster became the Mighty Thor and proved worthy to take Mjolnir for herself. Thor would use the axe until the conclusion of Jane's time as Thor, which ended when she sacrificed Mjolnir to destroy Mangog. Since then, Thor has retired the Jarnbjorn in lieu of utilizing hammers while he waits for a new mystical hammer to be made for him by the same Dwarves who forged Mjolnir.
THOR'S AXE IN AVENGERS: INFINITY WAR
After the Marvel Cinematic Universe's Mjolnir was destroyed by his sister Hela during the events of Thor: Ragnarok, Thor spent the rest of the film without any specific weapon. Instead, he spent most of the rest of the film learning to fully control his powers as the God of lightning, harnessing and amplifying his abilities.
However, he did receive a similar looking axe during the events of Avengers: Infinity War. Though, in an important distinction, it's not Jarnbjorn. Instead, the axe is the named Stormbreaker, which is the name of the hammer that Beta Ray Bill received during the course of the Walt Simonson's Thor run in the 1980s. The axe featured in the film also has a piece of Groot as the hilt of the weapon. While Jarnbjorn didn't show up in the strictest sense, it's hard not to consider his primary weapon as at least in part a reference to the axe.