Fifty years ago this month, the two most influential cult bands in rock history released their debut albums. The Velvet Underground's landmark The Velvet Underground & Nico dropped March 12, 1967, followed quickly by The Grateful Dead's self-titled debut on March 17, 1967.

Of all cult bands in history, no two have had a greater immediate and lasting impact on the direction of rock music. Countless artists cite them as the key influences, and multiple subgenres can be directly traced to either the Grateful Dead or the Velvet Underground. Yet unlike fellow '60s innovators like the Beatles or Bob Dylan, these two bands remain, for the most part, objects of cult adoration. No one likes just one or two Velvet Underground or Grateful Dead songs -- and if you're a fan of either band, chances are you're an overall music obsessive.

Despite this superficial similarity, the Velvets and the Dead couldn't be more diametrically opposed. The Velvet Underground's distorted, lo-fi dispatches from New York City's underbelly were a far cry from The Grateful Dead's psychedelic, bluesy hoedown in 1967. Bographically, the bands shared little in common. The Dead were from San Francisco; the VU hailed from New York City. The Dead flourished in the Haight-Ashbury hippie scene, which Lou Reed actively despised. The Dead took cues from blues, country and folk; the VU drew inspiration from early rock n' roll, R&B and avant drone music.

Even their album art exemplified this disparity. The Grateful Dead's cover was a wacky, visually stuffed collage; The Velvets' first album cover was a simple but quirky piece of pop art (a yellow banana with peel-able label) designed by Andy Warhol. On the Dead's album cover, Jerry Garcia smiled beneath an American flag top hat -- compare that to Lou Reed snarling at you from behind sunglasses on the back cover of The Velvet Underground & Nico.

And yet there were similarities. For starters: Drugs. The impact of illicit substances on both LPs is undeniable, although the Dead tended to celebrate the freewheeling hippie drug culture and its mind-expanding capabilities, while Lou Reed reveled in the danger and depression of addiction. Both bands were prone to circuitous instrumental tangents on stage, and both scaled back that part of their repertoire for the debut albums (with the notable exceptions of the lengthy "European Son" and "Viola Lee Blues," which close The Velvet Underground & Nico and The Grateful Dead, respectively). And both outsider rock outfits were fronted by a 1942-born man who suffered tragedy early in life: Within the same year, Garcia lost part of his middle finger and his father; as a teenager, Reed's parents subjected him to electroshock therapy for homosexual tendencies. Eerily, early incarnations of the Grateful Dead and the Velvet Underground went by the name "The Warlocks" at different points in their careers.

But to pretend Lou Reed and Jerry Garcia shared an alt-rock kinship, or were alternate sides of the same collector's coin, would be too glib. These two didn't share much in common when in came to music, but the fact that the Grateful Dead and the Velvet Underground both debuted on wax during March 1967 isn't just a coincidence, either -- 1967 was primed to be the year underground rock fired off its opening salvos.

Even though Bo Diddley had been experimenting with rock since its onset, it wasn't until 1965 -- a decade after debut singles from Chuck Berry and Little Richard -- that mainstream artists like the Beatles and Dylan started taking risks with rock on LPs such as Rubber Soul and Highway 61 Revisited, demonstrating both its sonic possibilities and the commercial potential of mixing avant inclinations with good ole rock n' roll. Perhaps not coincidentally, that was the same year Andy Warhol became interested in managing/funding the Velvet Underground, and it was also the year the Warlocks became the Grateful Dead.

But 1966 was the year that teed things up for both bands' debuts. With big-name artists taking chances on albums and succeeding wildly with critics and (for the most part) audiences (think Revolver, "Good Vibrations") the music business started investing in more adventurous bands, whether they had beards and wore tie-dye or sported leather and sunglasses. It's not a coincidence that iconic innovators like Jefferson Airplane and Frank Zappa (not to mention forgotten genre-benders like The United States of America and The Peanut Butter Conspiracy) all scored major label deals during this time. Execs saw a potential to cash in on the growing counterculture, and they cast a wide net to find the next big thing.

Obviously, that period produced a plethora of experimental-leaning rock classics. But in March of 1967, the Grateful Dead and the Velvet Underground achieved something unseen on albums like Are You Experienced?, Surrealistic Pillow and Sgt. Pepper's. Unlike those LPs, The Velvet Underground & Nico and The Grateful Dead didn't sound like mainstream albums with experimental flourishes -- they sounded like rock albums targeted squarely at a niche audience. They seemed to make the case that there was a future for bands who got off on jamming and/or harsh distortion. When Jefferson Airplane and the Beatles experimented, they kept one foot firmly in the pop world. The Dead and the Velvets, however, didn't seem to care about American Bandstand or the Billboard charts.

Of course, there was a precedent for this. One could argue Frank Zappa & the Mothers of Invention -- whose Freak Out! album simultaneously deconstructed rock while expanding its horizons in the summer of 1966 -- did the same thing nearly one year before either band's debut LP. But while Zappa opened doors for rock, his insular sonic palette didn't invite listeners to follow him -- much less start a band of their own. Attitude was a big part of that: Lou Reed was impossibly cool, Jerry Garcia seemed to be having the time of his life, but Zappa seemed bitter and supercilious -- it's no wonder he failed to inspire as many imitators as Reed or Garcia, despite being equally visionary.

The late '60s was a fertile time for rock, period. You could say it's hardly a shock that two pioneering underground rock groups debuted the same month. But there is something strange and special about two bands who inspired decades of underground admiration and imitation debuting within less than a week of each other. They might rule vastly disparate realms of rock, but both have established themselves as the kings of cult for decades to come.