Who was the first metal band?

Music historians usually point to Black Sabbath.

http://www.black-sabbath.com/

Black Sabbath are often cited as pioneers of heavy metal music. The band helped define the genre with releases such as Black Sabbath (1970), Paranoid (1970) and Master of Reality (1971). They were ranked by MTV as the "Greatest Metal Band" of all time, and placed second in VH1's "100 Greatest Artists of Hard Rock" list.

https://en.wikipedia.org/wiki/Black_Sabbath

There were a few groups which played individual songs that may be characterized as metal, but one of the first, if not the very first, to play that way pretty much all the time was Black Sabbath.

Black Sabbath:

"Black Sabbath formed in Aston, Birmingham, England in 1966 under the name Polka Tulk Blues Band (soon shortened to "Polka Tulk"), and later Earth, playing blues rock and hard rock."

Iron Butterfly:

"The band was formed in 1966 in San Diego and released their debut album, Heavy, in 1968, after signing a deal with ATCO, an Atlantic Records subsidiary."

Both WIKI references.

I vote Iron Butterfly!

Even more music historians point to "Led Zeppelin" as the first.

"Out of heavy metal various subgenres later evolved, many of which are referred to simply as "metal". As a result, "heavy metal" now has two distinct meanings: either the genre and all of its subgenres, or the original heavy metal bands of the 1970s style sometimes dubbed "traditional metal", as exemplified by Black Sabbath, Deep Purple, and Led Zeppelin."

https://en.wikipedia.org/wiki/Heavy_metal_music

"In 1968 that band went under the moniker "Earth" and began by playing charged blues. Soon the band evolved and became BLACK SABBATH. Based on all the votes sent in, Black Sabbath is by far the first metal band!"

metal-rules.com/polls/poll_3.htm no longer exists

Although Black Sabbath is the first band to actually be considered the first real band of the "Heavy Metal" genre of music, there are other influences on both them and the genre in general:

The Beatles recording of Helter Skelter (1968)
Cream (1966-1968)
Steppenwolf wrote the lyric "Heavy Metal Thunder"
Iron Butterfly - But they were more Acid Rock/Psychadelic than Metal
Led Zeppelin - Although they started out as the breakup of the Yardbirds (Jimmy Page owned the name), they were a blues band but heavier. The fact that they may have been considered a metal band came later.

According to this website, Cream were probably the first:

Heavy metal, that immortal hoary beast of lust, power and violence, was born in those murky last moments of the 1960s. The debate over who coined the term ‘heavy metal’ and which band was the first to bash out the initial fuzzed-out power chord will likely rage on forever ...

“Cream was the first definable heavy band,” claims Joe S Harrington, a full-contact rock journalist from Portland, Maine in the USA and author of the mammoth, and quite brilliant, Sonic Cool: The Birth & Death Of Rock’N’Roll, arguably the most complete and thorough examination of rock music ever written.

In that book he traced the beginnings of metal back to the power-blues of Cream’s Disraeli Gears album: “They had heavy solos, serious musicianship and Druidic imagery, all things that would become trademarks of metal years later. And this was still in 1966. However, metal didn’t start until two years later. By 1968 you had four bands that could definably be called heavy metal: MC5, Steppenwolf, Iron Butterfly and Blue Cheer.” All four left big footprints on the heavy rock trail. But only one of them can play the same song for an entire show.

https://www.loudersound.com/features/revolution-the-story-of-the-lost-pioneers-of-heavy-metal

A few heavy notables in '68 between Helter Skelter and Zeppelin's first album were

Love Sculpture - Blues Helping (album)
Taste - Blister on the Moon (single)

Love sculpture covers some classical pieces, that I dare say sound as heavy as the stuff on Sabbath's '71 album "Master of Reality". Provided they aren't original pieces, but the metal guitar is definitely there.

Guys sorry but the really first one was Alice Cooper in USA Black Sabbath relased their first album in 1970, but Alice in 1969 , and started his career in 1964. So I know anybody would say that Black Sabbath was the first band but i disagree.

Iron Butterfly was the band that sparked the coining of the label "heavy metal" from their first album "Heavy" and their name "Iron Butterfly". They formed in 1966 two years before Black Sabbath, Led Zeppelin, or Steppenwolf. Their first album was completed in 1967 but wasn't released until 1968 because of a management dispute. "Iron Butterfly Theme" is, in my theory, the first "heavy metal" song officially released on vinyl.

Although there's probably no definitive answer, a band not mentioned so far that came out in late 1967 is Blue Cheer. Their cover of Summertime Blues certainly contained distinct elements of metal still in use today.

https://en.wikipedia.org/wiki/Blue_Cheer