Pentagram was a great metal band that came out about the same time Black Sabbath did, the late '60's/early "70's. They both had a doomy approach to metal. While Sabbath was all doom and gloom, however, Pentagram was more up tempo and edgy. They were also into the heavy, euphoric, psychedelic rock of Blue Cheer, so that gave then a more lively edge than Sabbath.
They released very little material in the 1970's. Most of it has been recently re-issued on "First Daze Here: The Vintage Collection 1 and 2." That is a good set, with volume 1 being the best, as volume 2 is mostly demos.
Pentagram came back in full force in the 1980's with a much heavier and cleaner sound. This time around they were all doom, with crushing, frayed nerve-endings guitar riffs and the usual great vocals of Bobby Liebling. They were still way more up-tempo than Sabbath, but the lighter edge of their music was gone. They released 3 solid albums during this time: "Relentless", "Day of Reckoning", and "Be Forewarned", with "Relentless" being their heaviest.
Here's "Forever My Queen", from the 1970's:
And here's "Sign of the Wolf" from the 1980's album "Relentless".
Both of these tracks, are among my all time favorite songs. Enjoy!