It's hard to believe that 40 years have passed since rock legends Led Zeppelin released their cryptic album (long before the days of CDS) that featured cover art depicting a painting of an old man holding a cane, with a bundle of sticks tied to his back.

The painting hung on a wall covered with peeling leaf-patterned wallpaper. There was no title on the album cover and while it has been called different names, including 'Runes,' 'The Hermit' and 'ZoSo,' the most commonly used title is 'Led Zeppelin IV.'

To celebrate the 40th anniversary of one of rock's greatest albums, our brother site Ultimate Classic Rock has put together a commemorative four-piece package highlighted by a fascinating recreation of the album through YouTube clips of covers by a diverse range of bands.

Included in the tribute are Rollins Band taking on 'Four Sticks,' Zakk Wylde tackling 'Going to California' and Down bulldozing through "When the Levee Breaks.'

Ultimate Classic Rock also posted the FAQ 10 Things You Didn't Know About 'Led Zeppelin IV,' plus the site has posted a story about Zeppelin vocalist Robert Plant performing in the video for English opera star Alfie Boe’s cover of Tim Buckley's ‘Song to the Siren.’ And while you're checking out those three posts, enter here for your a chance to win a 'Zep IV' prize pack, which features the CD, a DVD set and the books '331/3 Led Zeppelin IV' by Erik Davis and 'Led Zeppelin FAQ' by George Case.

Majestic and musically diverse, 'Led Zeppelin IV' was the band's most popular album, selling 23 million copies in the U.S. alone and over 32 million worldwide. There's good reason for its acclaim. 'Led Zeppelin IV' features the band's catchiest and best written songs: the surging, sleazy and bombastic 'Black Dog,' the epic, immortal power ballad 'Stairway to Heaven' and the murky psychedelic blues of 'When the Levy Breaks,' with its unforgettable opening drum beat, which was sampled in 1986 by the Beastie Boys for the song 'Rhymin' and Stealin.'

Happy 40th! May the forest echo with laughter, evermore.