As a general rule, Thor tries to avoid inflicting mortal wounds on his enemies. This is particularly true in comics published during the Silver Age, when having a no-kill rule was a prerequisite for being a superhero. But, as Thor is an immortal battle god with incredible strength and a magical indestructible weapon, it should come as no surprise that he has occasionally had to let loose and murder his opponent(s). After all, when one's daily routine involves facing off against gods and god killers, sometimes the only way to end a threat is to end them.

RELATED: Totally Hammered: 15 Times Thor Was Completely Destroyed

In this article, we look at 15 instances when one Thor or another was backed against a wall and had no choice but to kill. While most of the deaths are treated with the appropriate amount of gravitas by the characters involved, it may be hard for readers to do the same; comics books are so resurrection-happy that, if anybody on this list hasn't been brought back to life, they probably will be soon enough. It says a lot about Thor's moral compass that he continues to view killing as a last resort even though he has to know that 90% of the people he kills will be back within a few years.

15 LOKI

Thor has been squabbling with Loki since before most other Marvel characters were born, so it was probably inevitable that at least one of their spats would end in one of them losing his life. In Thor #432, after another prolonged fight with his brother, Loki seems ready to surrender, only to then attack the wife of one of Thor's human friends for seemingly no reason.

Thor, who had already come close to killing Loki during the battle, finally loses it and sucks Loki's life force right out of him. What Thor didn't realize, however, was that Loki deliberately provoked Thor into killing him. Why? He'd made a deal with Mephisto stipulating that, upon Loki's death, his spirit would enter Odin's body, allowing Loki to take over Asgard.

14 GREGORY STARK

gregorystark

In the main Marvel universe, Tony Stark is the only child of Howard and Maria Stark. But in the Ultimates universe, he has a twin brother, Gregory, who has all of Tony's smarts and none of his vices -- or morals. Gregory even gives himself powers via nanites, which grant him superhuman strength and invulnerability. This is a big help to him in his various terrorist activities.

In Ultimate Avengers vs. New Ultimates #6, Iron Man detonates an EMP, knocking out Gregory's power-giving nanites and giving the Avengers a few precious moments to put a powerless Gregory out of commission. While Iron Man intended for one of his teammates to simply knock Gregory unconscious, an overenthusiastic Thor zaps him in the chest with a lightning bolt, frying him to a crisp.

13 THE SERPENT

According to the original Norse mythology, Thor is slated to die at Ragnarok after slaying Jormungandr, aka the World Serpent.  This story was loosely adapted by Marvel as Fear "Itself", wherein the Serpent is reimagined as Odin's villainous older brother, Cul, who has been imprisoned at the bottom of the Marianas Trench for millennia.  When he is freed by Red Skull's daughter, Sin, he can hardly wait to reunite with and/or assassinate his family.

Despite Odin doing everything, both logical and otherwise, to prevent his son from fulfilling the prophecy, Thor refuses to abandon his beloved Midgard to the danger posed by the Serpent. While his Avenger friends keep the Serpent's armies from wreaking havoc on Earth, Thor confronts his reptilian uncle.  The battle ends the only way it can: with both Thor and the Serpent dead.

12 MALEKITH

The big bad of Thor: The Dark World is Malekith, a Dark Elf bent on finding and merging with the Aether, a weapon powerful enough to control the Nine Realms.  Making the task of dominating the realms easier is the Convergence, a once-in-a-godly-lifetime event where the boundaries between the realms partially vanish, allowing Malekith easy access to all the worlds he could ever want.

His plan succeeds, up to a point. He manages to merge with the Aether before Thor's girlfriend, Jane Foster, figures out how to set up a teleportation device large enough to banish the incoming threat. She and Thor put this discovery to good use by zapping Malekith and his ship into another dimension. Malekith lands in Svartalfheim, where he is promptly squished flat by his damaged craft.

11 INTELLIGENCE SUPREME

When architect Eric Masterson took over the role of Thor in the early 1990s, he also took Thor's place on the Avengers and accompanied them into space during the "Operation: Galactic Storm" event. Unfortunately, our heroes are too late to stop the Intelligence Supreme, leader of an alien race called the Kree, from detonating a bomb that effectively wipes out his own people.

While half of the Avengers are more concerned with justice than revenge, the other half decides the only way to keep the galaxy safe is to kill the Intelligence Supreme. Thor joins this latter group in storming the Intelligence Supreme's headquarters and hitting him with all of their considerable combined might. While he does not deal the killing blow -- that job goes to the Black Knight -- it's doubtful if the Avengers could have accomplished their mission without Thor helping to weaken the Intelligence Supreme's defenses.

10 ASSORTED FROST GIANTS

Thor has undoubtedly slaughtered dozens, if not hundreds, of Frost Giants over the years, but perhaps no other killings led to more significant consequences than those committed in the 2011 film Thor. Ignoring Loki's advice, Thor leads a small, ill-fated expedition to Jotunheim in retaliation for some rogue Frost Giants breaking into the treasury in Asgard.

In Jotunheim, Thor makes a token effort at restraining himself before giving in to his desire to fight. Several Frost Giants meet an ugly death at the hands of Thor and his friends before a very irritated army surrounds the invaders.  Fortunately, Odin shows up to save their lives in the nick of time. It was this deadly incident that led Odin to decide that the only way to teach his son a lesson was to strip him of his powers and banish him to Midgard for a time.

9 RAGNAROK

clone thor

Ragnarok was the self-chosen name of the clone of Thor, who made a very memorable debut in Civil War #3 by killing the hero Goliath. The real Thor was a bit dead at the time, and when he returned and found out about Ragnarok's crimes, he was not at all happy. This acrimony came to a head when Thor and his doppelganger met for the final, fatal time in Thor #610.

Ragnarok, believing itself to be the true Prince of Asgard, attacks Thor's Asgardian friends, the Warriors Three. Thor is undaunted by the fact that Ragnarok survived having all of Asgard dropped on his head and really goes to town on the impostor. Their battle ends the way most lethal conflicts involving Thor do: with a whole lot of lightning.

8 THOSE WHO SIT ABOVE IN SHADOW

Despite being unable to come up with a name that's more than just a vague description, Those Who Sit Above in Shadow are among the most powerful beings in the universe. They get their power from the energies released by the Norse gods as they go about their lives, and particularly as the gods die in Ragnarok over and over again. As one might imagine, Those Who Sit Above in Shadow are deeply invested in making sure this cycle continues indefinitely.

Thor is willing to do whatever it takes to bring the shadow sitters' schemes to an end. To prevent his people from being manipulated further, Thor destroys a magic tapestry that both depicts and dictates the Asgardians' every move, thus breaking the cycle. With nothing left to sustain them, Those Who Sit Above in Shadow die along with the Asgardians.

7 SENTRY

Like a superpowered Dr. Jekyll, Robbie Reynolds has two distinct personalities. There is the Sentry, a well-loved superhero, and the Void, a mass murdering, Lovecraftian force of nature described by Norman Osborn as an "angel of death."  During the "Siege" event, Void has taken over Reynolds' mind and body and is working for Osborn.

In that capacity, he more than earns his keep. He tears apart the war god Ares with his bare hands; he brings the entirety of Asgard, which was floating just above rural Oklahoma, crashing down to Earth; and he kills Loki right in front of Thor. After all that, Reynolds regains control of himself long enough to beg the Avengers to kill him. Thor reluctantly obliges, electrocuting him and then depositing his charred corpse into the sun.

6 UTGARD-LOKI

Not to be confused with the God of Mischief, Utgard-Loki is -- or rather, was -- the ruler of Jotunheim, realm of the Frost Giants. He has also been called Skrymir, and this is the name he goes by in 2014's Thor #3. In this issue, Jane Foster, now known as Thor and wielding Mjolnir, must prevent Utgard-Loki and his legions from invading Earth in their quest to recover the skull of their king, Laufey.

Utgard-Loki, being a Frost Giant, decides simply encasing Thor in ice and swallowing her is an efficient way to end the danger she poses to him. What he fails to realize, however, is that Thor was still alive when he ate her. Thor uses Mjolnir to smash her way out, and if Utgard-Loki's skull is the price of her freedom, well, that's his problem.

5 ULIK

Ulik the Troll has been a recurring Thor villain since 1967. After Thor seemingly died in battle at the end of "Fear Itself", Ulik tries to take his place in Asgard as Tanarus, a new God of Thunder. But what happened to the real Thor, you ask? He's been eaten by a creature called the Demogorge, whose diet consists solely of gods, and robbed of his memories.

Thanks to the efforts of Loki and the Silver Surfer, Thor's hammer is restored to him, and with it come his memories and a desire to reclaim his rightful place as thunder god. Ulik is, as expected, unwilling to defer to anyone, least of all Thor. The two do battle, and the next time we see Ulik, he's been reduced to a very shiny skull.

4 BOR

In addition to the various other relatives he's been forced to kill, Thor is also responsible for the death of his grandfather, Bor, who is resurrected by Loki after being dead for centuries. Confused by the strangeness of 21st century Earth, Bor goes on a rampage through New York City. Thor tries to reason with him, but Bor comes to the erroneous conclusion that Thor murdered Odin and is someone he must extract vengeance from.

Concerned that their fight may hurt innocent civilians, Thor kills Bor, not realizing who it is he's been fighting until Balder, who was then serving as ruler of Asgard, tells him the bad news. Despite the mitigating circumstances, Asgard frowns upon those who would murder their king, and Thor is once again banished forever. The royals of Asgard are just one big happy family, aren't they?

3 DESAK STERIXIAN

Desak Sterixian isn't big on gods, and considering he lost his daughter when the god he used to worship demanded her in sacrifice, we can't say we blame him. But when he makes it his mission to destroy all gods, even those like Thor who aren't so cruel to the less powerful beings in their midst, Thor realizes he must put an end to Desak's deadly campaign once and for all.

Desak, however, is not an opponent to be underestimated.  At the time, Thor possessed both his own power as well as his dead father's unfathomable Odinpower, and yet he still couldn't so much as dent Desak's armor.  He likely would have ended up headless had not the Enchantress, eager to save the man she loved from certain death, sent the speedster Thialfi to deliver the aptly named Bloodaxe to Thor's hand.

2 SPIDER-MAN & THE THING

Thor: First Thunder is a retelling of Thor's origin and early days as a superhero. Loki, of course, looms large over Thor's earthly adventures and makes plenty of messes for his big brother to clean up. His final plot is to tinker with Thor's mind until all traces of mercy and decency disappear, subsumed by the desire to make humanity worship him as they once did. Thor does manage to snap out of it, but not before he murders both Spider-Man, who he flings into space, and the Thing, who he, ironically, clobbers to death.

But of course such popular characters can't stay dead. Odin is impressed by Thor's remorse and humility, and he not only brings the fallen heroes back to life, he also erases everyone's memories of Thor's murderous rampage, which surely saved everyone a lot of awkwardness at the Thing's poker nights.

1 RADIOACTIVE MAN

In Journey into Mystery #93, the Chinese government takes a long hard look at Thor and decides they need a superpowered defender of their own.  Accordingly, they turn to one of their top scientists, Chen Lu, and demand that he provide them with something powerful enough to knock Thor down a peg. Chen obeys, turning himself into the Radioactive Man and rushing off to New York to challenge Thor directly.

After being briefly hypnotized, somehow, by the radioactivity emitted by his foe, Thor regains the upper hand, using Mjolnir to create a whirlwind in which he captures Radioactive Man. Despite Radioactive Man's warning that Thor's actions will kill him, Thor does not stop, instead sending his nemesis flying back to China, where he ultimately detonates in a hopefully unpopulated mountain range.

Which of these murders is the most shocking? Let us know in the comments!