Tool are probably the biggest band on this list and depending on who you ask (and where in their discography you’re looking), they could classify as progressive metal or progressive rock. Their earlier albums are considerably rawer than their later ones, though, and as raucous as 1993’s Undertow gets, nothing on it matches the sheer hostility of “Hooker With a Penis” from 1996’s Ænima.

It’s fairly sophisticated yet uncharacteristically straightforward, with combative rhythms and beastly guitarwork that don’t let up.

That said, it’s frontman Maynard James Keenan’s downright belligerent tell-offs to haters that seal the deal. He pretty much yells with gruff distortion the entire time, and he’s never been more confrontationally vulgar (“I’m the man and you’re the man / . . . So you can point that fuckin’ finger up your ass / All you know about me is what I’ve sold you, dumb fuck / I sold out long before you’d ever even heard my name / I sold my soul to make a record, dipshit”).

There are no breaks from the anarchy, with Tool evoking the pissed-off nature of Slipknot more than they do the tranquility and playfulness of prog influences such as Pink Floyd, King Crimson, Yes and Rush.

As a top-tier progressive death metal act, there’s no denying that Opeth have a ton of extremely savage music. Although there might be moments on songs such as “Deliverance,” “Blackwater Park,” “Advent” and “In Mist She Was Standing” that are slightly heavier than anything on “Heir Apparent,” all of them are offset by at least one or two substantially serene detours.

In contrast, this cut from their ninth “observation” – 2008’s Watershed – is essentially gnarly from start to finish.

“Heir Apparent” is far from the Swedish quintet’s greatest track, but it’s the perfect example of how unrelentingly calamitous they can be. It begins with perhaps their most ominously thunderous and suspenseful opening to date, and after a brief piano interlude, it launches headfirst into a booming onslaught of antagonistic arrangements and devilish proclamations. Each instrument barrels along with foreboding fury as creative architect Mikael Åkerfeldt unleashes his foulest growls.

Even the fleeting acoustic breaks are noticeably menacing compared to the lulls within Opeth’s other material, so there’s darkness strewn throughout almost every second of its nine-minute run.

After focusing mainly on orchestral/progressive/alternative rock with 2002’s Six Degrees of Inner Turbulence, Dream Theater went in a significantly different direction with 2003’s Train of Thought. As its cover suggests, it’s a darker and dirtier record that pays homage to the band’s 1970s and 1980s heavy metal forefathers as much as it does the prog rock gods of yesteryear. In fact, it might still be Dream Theater’s heaviest LP and a major reason why is “This Dying Soul.”

Centering on the fourth and fifth steps in drummer Mike Portnoy’s “Twelve-Step Suite” (“Reflections of Reality (Revisited)” and “Release”), the piece is a stampeding hybrid of hyperactive percussion, roaring guitarwork and acidic effects/tones from the jump.

Yes, it ebbs and flows in intensity afterward – with some gorgeously introspective passages here and there – but it maintains its intimidating wrath until the end.

What really pushes “This Dying Soul” to the edge is vocalist James LaBrie’s intentionally fuzzy nu-metal rapping (“Running power mad with no control / Fighting for the credit they once stole / No one can ever tell you what to do / Ruling other’s lives while they can’t stand the thought of you!”). We’re not saying it’s necessarily good (actually, it’s quite divisive amongst fans), but it does see LaBrie reaching a newfound level of brazen indignation.

Given how atmospheric and baroque much of Leprous’ modern music is (venturing into progressive/art rock as much as it does progressive metal), it’s startling to hear how hellish they could be during their initial few years and first three studio sets.

Undoubtedly, a big part of that comes from the fact that operatic frontman Einar Solberg is the brother-in-law of Emperor frontman/guitarist Ihsahn (who sung on several early Leprous tunes).

Case in point: “Contaminate Me,” the closing composition of 2013’s Coal and the fiercest thing Leprous has ever done.

To be clear, Solberg’s soaring singing is typically booming but vulnerable (so he’s not what makes “Contaminate Me” surprisingly sharp). The Meshuggah-esque roughness that surrounds him, however, absolutely is, with his bandmates rarely diving into the divine intervals Leprous would come to be known for. Even when they do, it’s with unwieldy black metal dissonance, and appropriately, Ihsahn’s screeches coat their calming segues with horrifyingly guttural statements.

If you played “Contaminate Me” for someone without context, they’d be shocked to learn that it’s a Leprous track.

When you think of the first progressive metal pioneer, you likely think of Fates Warning. (Okay, maybe Queensrÿche come to mind before them, but Fates Warning are at least a close second!) After all, 1985’s The Spectre Within and especially 1986’s Awaken the Guardian hinted at what the genre would become by the start of the 1990s.

On the other hand, the band’s 1984 debut LP – Night on Bröcken – was pure heavy metal and it’s there that Fates Warning fully committed to their aggressive tendencies via “Misfit.”

Obviously, it has nothing to do with the New Jersey band of the same name, yet ironically (or coincidentally) enough, “Misfit” has as much hardcore punk feistiness as it does heavy metal coarseness. Original singer John Arch belts out verses and choruses with the piercing range of Bruce Dickinson and King Diamond; meanwhile, the rhythm section charges forward without hesitation as guitarists Jim Matheos and Victor Arduini overlap and exchange blistering solos and crunchy riffs.

All things considered, “Misfit” is heavy metal in its most traditional form, but it’s also Fates Warning’s peak balls-to-the-wall configuration.