No-one's mentioning any of the stuff that I like, so I feel compelled to post here.
Firstly - CELTIC FROST. Every single heavy metal band that has ever experimented with... well, anything really, owe their existence to Celtic Frost, who did everything before everyone else, and even did a few things that no other metal band has ever dared since.
That's a good song but it's mindblowing to think that it was recorded in 1986. Nobody was doing this back then. Their record label hated that album and so did the fans at the time, but Into The Pandemonium is now considered the single album that defined orchestral doom metal and the list of imitators is huge and certainly includes all those crappy prog bands everybody mystifyingly loves.
Also, SEPULTURA.
In Brazil metal actually has the type of socio-political relevance that punk had at one point in England, so it's fitting that the best of the original thrash metal bands was from there, and they were lyrically and musically ahead of the pack so far it just wasn't funny. Metallica had to write cheesy pop songs (albiet with heavy guitars) to break on the charts internationally. Sepultura did the same thing years later with a defiantly anti-commercial song that was 90% built around one fucking note:
And let's not forget ANAL ****, who are particularly relevant for forum users.
These guys invented trolling before there was even an Internet to troll on. If you consider yourself a troll and you don't have an Anal **** album in your collection, you could use some lessons from the masters. They got their record deal by trolling the record company, who fortunately had a sense of humour. After releasing a few albums and annoying the world with violent misogyny and hateful grindcore, they started to build up a following, so the band trolled them too by releasing an album full of pro-feminist acoustic ballads:
There's a lot more great metal bands I could think of but these are glaring omissions that will fill the void for now. Enjoy.