Led Zeppelin is widely considered to be one of the greatest ever rock'n'roll bands. But it is well known that they stole a lot of material from older acts, particularly black American blues musicians, and rarely gave any credit for it. So what makes them so important?
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It's true that Led Zeppelin were notorious music thieves (with "Lemon Song" being a particularly infamous example). Like many other British musicians of the time, they had an unpleasant tendency to treat black American music as if it was a freely available natural resource, available to be plundered, and only under the domain of copyright after some white artist had claimed it.
However, it would be wrong to dismiss them as being purely derivative. Although they pulled heavily on a wide variety of sources from Tolkien, to British folk music, to the blues, they created a distinctively original and influential synthesis that is often credited with birthing the "heavy metal" genre, and that arguably continues to sound fresh and new even today.
For reasons partly related to general societal racial bias and partly a reflection of affinity-based market demographics, the past century's history of popular music was littered with examples of white musicians gaining fame and fortune on the back of songs, styles and entire genres that were created or innovated by black musicians --who often continued to labor in poverty and obscurity in spite of their genius. So, being white interpreters of a black musical tradition is a definite factor that cannot be denied in the Led Zeppelin success story. But they were also amazing musicians who made their own indelible contribution to musical history --you can't mistake them for anyone else, including their own influences.