These two masters of the low end aren't just driving sonic forces of their respective bands, both bassists are primary writers for their groups, as well.

Geezer Butler is perhaps the world's first true metal bassist. Even when placed next to the phenomenal Tony Iommi onstage, Butler's bass technique is not dulled one bit by Iommi's immortal riffing. Though rooted heavily in groove, Butler's technical proficiency is not to be underestimated. More than 40 years into Black Sabbath's existence, Geezer continues to lay down some of the most memorable bass lines in metal history.

Overkill bassist D.D. Verni has a tough battle in Round 1 of our Greatest Metal Bassist tournament. Verni is fairly underrated as a bassist, but any Overkill fanatic will tell you that Verni is the heart of that band. The artist has delivered some of thrash metal's best riffs and grooves, along with acting as a background vocalist and onstage leader.

Geezer Butler or D.D. Verni? Vote for your favorite bassist in the poll below! Voting for this round closes on Sunday, Sept. 29 at 11:59PM ET. Fans can vote once per hour, so keep coming back to make sure that your favorite metal musician wins!

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