The enchantment on Thor's hammer Mjolnir means that only those who are truly worthy can lift it - a fact which has made doing so the ultimate symbol of heroism in Marvel lore. Only select heroes such as Captain America, Beta Ray Bill and DC's Wonder Woman have proved to be heroic enough to manage it, and the original plans for Marvel's World War Hulk would have added a new name to this illustrious roll call.
Cast by Odin, the enchantment on Thor's hammer has since taken on a life of its own, but it seems to reliably respond to those who are both pure of heart in fighting to protect others, and who battle on the frontlines of the galaxy's most significant conflicts. One such conflict was World War Hulk, when Bruce Banner's superstrong alter-ego returned to Earth seeking vengeance on the heroes who had exiled him in space and - he believed - caused the death of his wife when the ship they used later exploded. While Hulk's thirst for revenge was terrifying, it was also righteous, and several Marvel heroes eventually stood by his side to seek justice for what the secretive Illuminati had put him through.
However, it's an ally Hulk brought with him from space that was meant to be revealed as worthy of Mjolnir. In an article on the planning for World War Hulk on his blog, The Tom Brevoort Experience, the titular Marvel editor shares an overview of the event penned by Grek Pak (who wrote it, with art by John Romita Jr.) Many details are different from the final story, including the involvement of Thor, who was ultimately indisposed on his own adventures when the event was published. It's a huge shame that was the case - both because a tie-in What If? story showed that Thor could have brought the invasion to a peaceful conclusion, and because his early intervention would have revealed that Korg the Kronan is worthy of Mjolnir.
Thor leaves his stronghold in the Oklahoma desert, heads towards the Hulk. Korg is the one to meet him. Old adversaries. Korg tells Thor that the Hulk is right. Thor should stand down. Thor knocks him aside. The Hulk comes out. Great clash over the desert. Epic, earth-shattering battle. Ends with the Hulk making Thor drop his hammer - and Korg picks it up. Korg actually picks up the Hulk’s [sic] hammer - he’s worthy. Thor’s blow [sic] away by this. He and the Hulk have a moment. Thor withdraws, says he doesn’t understand this all. But he won’t fight these heroes.
Korg Was Meant To Be Worthy of Mjolnir
MCU fans will know Korg from Thor: Ragnarok and subsequent films, where he's voiced by director Taika Waititi, however his comic history goes all the way back to 1962's Journey into Mystery #83, and the very first appearance of Thor. In 'The Mighty Thor and the Stone Men from Saturn!' - by Stan Lee, Larry Lieber, and Jack Kirby - Thor's original villains are a squad of Kronan invaders. In Planet Hulk, Hulk meets one of these warriors in the Red King's arena, and the two become Warbound, forging a bond of unbreakable loyalty that continues in World War Hulk. It's for this reason that Korg being worthy of Mjolnir is such a perfect moment, as Thor is shown the righteousness of Hulk's cause by realizing that in fighting for Hulk, his first Earthly enemy is truly worthy.
Marvel Needs to Bring Back Korg's Worthiness
Sadly, changes to the story meant this moment was lost, and Korg has yet to canonically get the honor of lifting Mjolnir (indeed, the event would ultimately show Earth's heroes being a lot less open to Hulk's point of view.) Hopefully, Marvel revisits this concept, as it's a fascinating way to pay off Korg's connection to Thor, and a tribute to a character whose honor, kindness and sense of duty makes him worthy of Mjolnir whether Marvel chooses to show it or not.
Source: The Tom Brevoort Experience