1
Paranoid Black Sabbath

The most influential band ever! They have been huge influence for all of the extreme metal bands. Especially, after the end of hair metal foolishness, people rediscovered them with the rise of thrash, and then death metal. They basically wrote the first ever Doom Metal song. They are the first band who wrote dark, shocking lyrics. The list is endless... And they were also influential for stoner rock, other softer metal bands and some of the nu-metal bands.

2
Sad Wings of Destiny Judas Priest

Even though the influence of Judas Priest sound on particularly "extreme" metal is somewhat questionable. It's a fact that all of today's metal bands were huge fans of the Priest.

3
Ace of Spades Motörhead

When Motorhead first came out in mid 70s, they were different from all the bands around with Lemmy's ugly vocals and unique bass playing. "Ace of Spades" still remains one of the best metal songs ever written. Even hough Lemmy can't match the quality of albums like "Ace of Spades", "Overkill" and "Bomber" any longer, the impact Motorhead did on extreme metal is unqestionable.

4
The Number of the Beast Iron Maiden

The monster band, Iron Maiden is the reason why many people started listening to heavy metal music. They may not be much related to extreme metal sound, but still we can see their influence on melodic death metal bands and some of the black metal bands.

5
Angel Witch Angel Witch

The reason I put this NWOBHM band is their self-totled debut album, "Angel Witch". Even though, their career was cut short, bands like Metallica, Slayer and Candlemass were influenced by them.

6
Black Metal Venom

Venom is an obvious choice here. When they first came out in early 80s, the first noticable thing about the band was their openly satanic image. All of the critics hated the infamous trio and were always nominated as the worst band many times. Well, Black Metal wouldn't have existed if it weren't for them.

7
Born Too Late Saint Vitus

Many doom metal bands owe a lot to St. Vitus, as they were doing the ultra-slow, first-album-Sabbath dirge long before it became fashionable. The band has been fortunate to feature three great vocalists including Wino throughout their career.

8
Day of Reckoning Pentagram

Pentagram, inspired greatly by Black Sabbath, was essentially formed in 1972 but their first album was recorded in 1985. They have become pioneers of doom and stoner metal.

9
Don't Break the Oath Mercyful Fate

Mercyful Fate from Denmark in the early 80's was one of the most important metal bands of the decade. Characterized by the unique, operatic vocals of King Diamond, openly Satanic lyrics, and crushing riffs by the guitarist duo of Hank Shermann and Michael Denner, the band's first two full-length albums (Melissa and Don't Break The Oath) are essential 80's metal classics, with their lyrical stance causing quite the controversy at the time. Their influence on extreme metal genres (both sound and lyricswise) was huge and they deserve their spot in the list without a doubt.

10
St. Anger Metallica

Well, I don't know what to say about Metallica... They spearheaded the thrash metal music, made extreme music well known all around the world, recorded all time classic albums (Master of Puppets, Ride the Lightning)and were huge between 1983-1991, then became sellouts after their 91 self-titled album, changed their image and sound to cope with grunge era, backstabbed their fans by attacking Napster, and finally they hit rock bottom with "St. Anger". Who knows what awaits them in the near future? But I'm pretty sure that they are the reason we are listening to a lot of quality extreme metal bands today.

11
Reign in Blood Slayer

I remember listening to Slayer's "Hell Awaits" album for the first time. I was like "Man! This is the heaviest thing I've ever listened to" . They were the most extreme and heavy band around at that time. Even though they were a part of Big 4 (Metallica, Anthrax, Megadeth), they were different from the other 3. Actually some people created a genre called "Speed Metal" associated with Slayer. They are without a doubt legendary and they influenced every single extreme metal band.

12
To Mega Therion Celtic Frost

An enormously influential band in the field of particularly black/occult metal. Celtic Frost, formerly known as Hellhammer, with founder Tom Warrior were continously in a progressive songwiting mode and he recorded albums that were ahead of their time. The essence of Celtic Frost is best captured in the first three albums, with Morbid Tales being the most raw, Into the Pandemonium the most experimental, and To Mega Theron being the most consistent and probably the best representation of the band's style. It's easy to acknowledge Celtic Frost's influence by just looking at the sheer number of Celtic Frost songs covered by today's extreme metal bands.

13
Seven Churches Possessed

Possessed, pioneers of death metal, took an early Slayer influence to another level of rawness and brutality. Their "Seven Churches" debut remains an early death classic. Their career was cut short because of the tragic shooting accident of Jeff Becerra. Personally, I'm not a big fan of Possessed, but if the accident had not happened they might have improved their sound over the time.

14
Nothingface Voivod

I'm a huge fan of Voivod and i believe they are one of the most underrated bands in metal. They started out with a chaotic raw thrash metal sound in the early 80s, and then they progressed their sound with excellent releases (Killing Technology, Dimension Hatross, Nothing Face). The music they made was called "techno-thrash", which combined technical dispozitiv playing with thrash metal and added Pink Floyd and Rush influences into the mix with sci-fi lyrics. And then they softened a little bit with Angel Rat and Outer Limits (both are great albums). Then Voivod lost their voice "Snake" and released mediocre and not progressive 2 studio albums with a different singer. Now Snake is back with the addition of Jason Newstead and they released a solid self-titled album. Voivod remains a legendary band among musicians and they influenced a lot extreme metal bands with their technicality.

15
Hammerheart Bathory

Bathory, a one-man band (Quorthon), must be considered a major influence on two extreme metal genres. First, with his first two albums, he created black metal. It was Bathory, along with Venom, who helped pioneered the raw death/black style and gutteral vocals that are now standard in the genres.
Second, he created the genre called Viking Metal with his later work. He recorded epic albums such as "Hammerheart" and "Blood, Fire, Death". Unfortunately, Quorthon passed away in June, 2004, which is a huge loss for extreme metal community... Rest in Peace, Quorthon and I hope you are in Valhalla.

16
The Sound of Perseverance Death

The band "Death" basically named the genre. Their debut album "Scream Bloody Gore" was the heaviest thing that i've ever listened to at the time it was released. Even though, it was raw and primitive, it featured solid songwriting. With each release Death improved their sound and became a technical Death Metal band. Death or Chuck Schuldiner released seven studio albums before he passed away on DEcember 31, 2001 with brain tumor and none of these albums were close to mediocre. My favorites being Spiritual Healing and Individual Thoughts Patterns. I am pretty sure that if he was alive, he would keep on releasing great albums. RIP Chuck! You are dearly missed.

17
Nightfall Candlemass

Candlemass, influenced by Black Sabbath (who isn't) and Angel Witch, is one of the founders of the modern doom metal movement. Their debut, Epicus Doomicus Metallicus, is an incredible doom metal album with great songs like Sorcerer's Pledge, Solitude, and Demon's Gate. However, the arrival of vocalist Messiah Marcolin created the band's trademark sound with his amazing opera style vocals. With Marcolin they released three great studio albums Nightfall, Ancient Dreams, and Tales Of Creation, with Nightfall being a classic. Unfortunately, their reign did not last long and Marcolin departed and the band couldn't recover.

18
Scum Napalm Death

Napalm Death are the creators of Grindcore period. However, more important than that they influenced a ton of bands that were into any kind of extreme metal music. Just look at their original members and what they did after they quit ND... Lee Dorian (vocals) formed Cathedral, one of the best in Doom; Justin Broadrick (guitar) formed Godflesh, one of the best in Industrial, Bill Steer (guitar) formed Carcass, founders of Gore metal. In addition to this impressive list, the other members of Napalm Death involved in a lot of experimental side projects.

19
Clandestine Entombed

Entombed spearheaded the first wave of Sweedish Death Metal sound with their first two albums, Left Hand Path and Clandestine. Both are considered as Death Metal classics by critics. (We see some bands nowadays who pay tribute to their early sound, e.g. Chaosbreed, Bloodbath) But they weren't satisfied with this and moved into different territories and created a style called death roll with adding rock'n'roll flavor to their sound. This decision angered many of their fans but I loved everything they released so far.

20
De Mysteriis Dom Sathanas Mayhem

I must admit that I was never a fan of early raw and primitive Negru Metal sound. But you have to give Mayhem their due. They are the originators of this sound. Musicians such as Hellhammer, Varg Vikernes and Euronymous who played in Mayhem are influential personalities in Black Metal. Mayhem was also the center of controversy and crime in Norway. But this is not the place to talk about this.