The heralds of Galactus are a complicated bunch. Some willingly go grocery shopping for the planet-eating cosmic entity. Others, not so much. Throughout time and space, they have varied in their commitment to their calling, their power and their use of it.
While a few heralds find their way to freedom and heroism like the Silver Surfer, others engage in behavior that even Galactus sometimes finds too much (which is saying a lot).
10 Herald of Thunder
A pretty awful thing the most recent Herald of Galactus did was simply take the job. Thor may have had his reasons for doing so, but choosing to find planets for Galactus to eat isn't exactly the noblest thing to do. Thor took the job to stop the Black Winter, the same calamity which destroyed the universe Galactus originally hails from. He became the Herald of Thunder, and one imagines he's going to get a talking-to from his friends and allies once word gets around.
9 So Bad He Got Fired
You've got to be bad to get fired from your job. And you've got to be super evil to give Galactus the heebies. But that's what The Fallen One did. The second of the Heralds, The Fallen One was vested with dark energy rather than the Power Cosmic. This may have made him a little too good - or bad - at his job. His cruelty and depravity toward the people of the early universe ultimately led Galactus to pink slip the guy and confine him in a prison called the Kyln. Naturally, he later escaped.
8 Terrax Takes Manhattan
After the Silver Surfer and Galactus parted ways, Galactus wanted a Herald who wouldn't turn their nose up at finding planets full of sentient beings for him to eat. He got that and more in Terrax the Destroyer. Already a certified jerk before he got called up to the majors, Terrax used his power to move stones with his mind to drag planets onto the dinner table. He also wanted even more power, so he took over Manhattan and held the city hostage, demanding the Fantastic Four destroy Galactus worldship. As a result, Galactus sent Terrax back down to the minors and took the Power Cosmic from him.
7 Shifting Focus
Red Shift became Galactus Herald for a time in the 90s when everything was so extreme. Consequently, Red Shift had grander ambitions than the others. One of those was to put Earth back on the menu after Galactus had generally avoided it after his first run-in with the Fantastic Four.
This caught the attention of the Silver Surfer. Red Shift trapped the both of them in a black hole and they duked it out until Norrin Radd broke loose with some pent up cosmic energy. Red Shift remained trapped inside, unable to escape and becoming another forgotten 90s villain.
6 She Simply Dazzled
Remember how Terrax took over Manhattan? Well, that only happened because of Dazzler. Maybe that's putting too much on her. Her brief time as a Herald only served one purpose: to find Terrax. The despicable but cowardly villain hid in a black hole from Galactus and the big purple guy drafted Dazzler to light him up. It's unclear why Galactus went with her if her ability to illuminate a black hole should make her more powerful than he is.
5 Just Didn't Care
Galactus seeks out new Heralds more often than Darth Sidious seduces new Sith apprentices. After parting ways with Terrax (and Nova) Galactus eventually settled on Morg the Executioner. Like Terrax but somehow worse, Morg was no stranger to death as his name implies. An executioner on his homeworld, he simply shrugged and was like, "whatever," when Galactus showed up. Watching everyone and everything he ever knew turn into Galactus-Chow was no big deal for Morg and he gladly took on the role of Herald.
4 Tyrannical
While debatable as to whether he was a Herald, Tyrant largely served the same function. Galactus created this living machine to find him worlds to devour, but Tyrant, like a lot of artificial intelligence, develops ideas of his own. He goes on a conquering spree through the early universe and Galactus, a big stickler for healthy portion sizes, goes to war with him. Galactus depowers him and casts him into a forgotten part of the universe. However, like all bad guys thought forgotten, Tyrant came back.
3 Shades Of Gray
Silver Surfer is one of the greatest and most noble heroes in the Marvel universe, but he was a Herald of Galactus, and this means he did bad things. Not all of it was by choice, though. His Faustian bargain spared his homeworld, but after Norrin Radd ran out of uninhabited planets for Galactus to feed on, things got dark.
Granted, Galactus messed with the Silver Surfer's mind to get him to deliver inhabited worlds, but it still happened, and it was tragic for all involved. The Surfer only broke free of his master's hold when he chanced upon Earth and encountered humanity.
2 The Last Herald?
Nova served as Herald for a time in the 80s, replacing Terrax, but her greatest story is one that exists essentially out of continuity and remains sadly unfinished. John Byrne wrote and penciled 'The Last Galactus Story" in Epic Comics, imaging a Marvel Universe billions of years in the future. Stars go out. Galaxies shutter. Galactus and Nova investigate and are drawn into a war for all time with a Watcher. As the universe collapses, Galactus sacrifices his energy - or he would have, had the story finished and Nova inherits it. She becomes a new Galactus in a new universe, starting the cycle over.
1 Dust To Dust
The absolute worst Herald is Stardust. A fanatical zealot, he went far beyond finding planets for Galactus to eat. Even after those planets were destroyed, he hunted down and killed any survivors from those worlds to ensure no one ever found what happened to them (though you'd think word of Galactus would be well circulated by that point). Stardust's bloodlust runs into a snag when he hunts down Korbonite survivors and runs headlong into Beta Ray Bill. It didn't exactly work out for anybody, as Stardust opened a dimensional gateway and released an alien hell-demon.