Some persistent misinformation involving "Black Dog" has been floating around for quite some time now. The first point is that "Black Dog," which opens Led Zeppelin's untitled 1971 album, borrowed too heavily from Fleetwood Mac's "Oh Well." Not only is this point groundless, I would argue that "Black Dog" is one of Led Zeppelin's most original songs. It's off in its own world with its winding riff and complex time signature changes. Of course, it's possible to cite songs that influenced John Paul Jones, Jimmy Page and Robert Plant to write this song, but to suggest "Black Dog" was plagiarized is off the mark. It's ironic when an apologist for the band implies wrongdoing where none exists. Dave Lewis states that Jimmy Page "would admit years later" that the vocal part for "Black Dog" was influenced by "Oh Well."
[1] Led Zeppelin were clearly fans of Fleetwood Mac, particularly when that band was primarily a blues band under the leadership of Peter Green. Had it not been for Fleetwood Mac, Led Zeppelin might not have come up with "Rock and Roll" or the vocal part for "Black Dog," as Robert Godwin suggests.
[2] Fleetwood Mac's influence can certainly be heard in these songs, as well as "The Lemon Song." Still, there's nothing to "admit" here. "Oh Well" and "Black Dog" have a similar call-and-response dynamic between vocalist and the band, and the two songs share a similar theme, but that's a far cry from plagiarism. Riff-driven, blues-based call-and-response songs are not uncommon in rock music, particularly around the time Led Zeppelin recorded "Black Dog." In fact, a reader once wrote to me expressing the view that Led Zeppelin used the Who's interpretation of Mose Allison's "Young Man Blues" as inspiration for "Black Dog." As he put it, "Is there anyone out there who really believes "Black Dog" is NOT a thinly veiled redo of the Who's version of Mose Allison's "Young Man Blues" from Live at Leeds? The song structure is identical. The main riff is almost identical. Hell, it's even written in the same key." While this may have been a common motif for songs at the time, it's only a basic structure.
The second point of misinformation about "Black Dog" is that the riff was inspired by Muddy Waters' 1968 album Electric Mud. Keith Shadwick
[3] and Andy Fyfe
[4] both repeat this erroneous detail. In the December, 2007, issue of Mojo, however, John Paul Jones states that he wrote the main riff for "Black Dog" after listening to This Is Howlin' Wolf's New Album.
[5] That authors of such definitive books about Led Zeppelin repeated this misinformation is understandable, as it was John Paul Jones himself who for years had misstated the origins of the "Black Dog" riff in interviews. As Steve Sauer explains, John Paul Jones had confused Electric Mud and This Is Howlin' Wolf's New Album, but didn't realize his mistake until Sauer tracked him down with a copy of This Is Howlin' Wolf's New Album in his hand. After listening to both albums closely Sauer realized that it was "Smokestack Lightning" from This Is Howlin' Wolf's New Album that had inspired "Black Dog."
[6] And it's not all that surprising that John Paul Jones mixed up Electric Mud and This Is Howlin' Wolf's New Album. Both albums were late-1960s attempts to "update" the sound of these blues artists by incorporating more psychedelic instrumentation. While both albums have interesting tracks to recommmend them, you can tell that neither artist's heart was completely into this new sound.
In fact, Howlin' Wolf's album explicitly stated the artist's disdain for the record on the cover. This Is Howlin' Wolf's New Album also contains spoken interludes where Howlin' Wolf explains why he doesn't like his new album. One of his complaints was that electric guitars make "queer sounds." But John Paul Jones listened closely to "Smokestack Lightning" and was inspired by what he heard. The track had "a blues lick that went round and round and didn't end when you thought it was going to."
[7] Using that approach he developed the riff for "Black Dog," stretching out the pattern over several measures and incorporating a number of time signature changes, which has made this one of the most difficult songs to cover by the Hampton String Quartet, a chamber group that covers rock songs.
[8] So while it may be possible to cite sources of inspiration for "Black Dog," this track is Led Zeppelin's original work.
Recommended Listening
 
Howlin' Wolf - This Is Howlin' Wolf's New Album
 
Fleetwood Mac - Live in Boston Remastered Vol. 2
 
The Who - Live at Leeds
Compilations of Original Versions
None of the compilations is concerned with the origins of "Black Dog\.