Probably the most famous issue of Walt Simonson's run on Thor (I figure either the Beta Ray Bill issues that started it or the all-splash-page fight with the Midgard Serpent are the other two candidates.) Thor led a host of Asgardian warriors into Hel to recover a bunch of mortal souls Hela isn't supposed to have. Noble as that is, Thor's also trying to avoid dealing with Odin being locked in battle with Surtur somewhere he can't reach. Plus the fact he said some harsh things to Sif while under the control of Enchantress' sister, Lorelei.
The mission's a rough go, as you'd expect when trying to steal from a death goddess. Some of the Einherjar are lured to their doom by visions of their loved ones. Balder's trying to hold it together since he barely made it out of Hel once before, and was a traumatized wreck for months after. Having his dead wife try kill him while proclaiming her hatred isn't helping. Although Thor finds out she lied to help Balder move on from her. Not sure how sound a strategy that is. Thor ultimately challenges Hela to a fight, one-on-one, for the souls. He wins, but she just about pimp slaps the lower half of his face off.
Still, souls won, and Hela having sworn to let them leave, it's time to go. Then Hela pops up, bringing along Skurge the Executioner. He was part of the army, but broke off when he found the Enchantress waiting. Balder reminds him things often aren't as they seem, and Skurge cuts through the illusion, revealing someone named Mordonna. Hela offers Skurge a job sailing the ship of the damned (made from the fingernails of the dead) once it's finished. She's actually hoping he'll attack her, so she can attack Thor and the others without breaking her word. Wonder what she'd have done if he shrugged and said, "Sure, mama always wanted me to be a sailor man."
Someone like Thor. Or, well, no, Skurge sucker-punches Thor. Nobody's real happy about that, but he explains he's going to hold the bridge instead. He's tired of feeling like everyone jerks him around and plays him for a sap, the Enchantress at the top of that list. So, rather than go back to that life, to letting himself be led around by the nose and losing all his self-respect, he's going out in a blaze of glory. And he does. Not one of Hela's forces gets past him, even at cost of his life. His stand apparently so heroic, that even Hela herself bows to him (and later allows him to leave for a happier realm of the dead, claiming one as noble as he doesn't belong there.)
Safely away, the Asgardians return home to their families and ruined homes, while Thor ferries the souls back to Earth. While there, he's going to get roped into a combination Secret Wars II tie-in/Power Pack team-up. Then he gets turned into a frog. Being turned into a frog doesn't do much to stop him from beating Loki's face in.
We never actually see the extent of the damage Hela does to Thor's face. Either he covers it with a piece of his cape, or its kept in shadow when he shows others. Two drunks that tried mouthing off to him lose their lunches at the sight. Eventually, he grows a beard, which he maintains for the remainder of Simonson's run. DeFalco and Frenz shave it off immediately, revealing his wounds have healed. Skurge pops up again late in Simonson's run, when Thor has reason to settle some things with Hela.
[11th longbox, 117th comic. The Mighty Thor #362, by Walt Simonson (writer/artist), Max Scheele (colorist), John Workman Jr. (letterer)]