This past Saturday, Slim Thug decided to break plenty of hearts among Houston rap fans.

He announced on Instagram that his King & a Boss album, that long-awaited disc between he and enemy-turned-BFF Z-Ro, wasn't coming out. Thanks to timing, the proposed project had lost a bit of its luster from when it was originally announced on the heels of recent collaborations "Summertime" and "Lovin' You."

They still paired off together perfectly; imposing figures on two fronts. You weren't going to duck around a Slim Thug verse without Z-Ro punching you in the throat via a chorus or verse of his own.

That's kind of the novelty of a pair-up, though. For every Killer Mike & El-P that brings us joy via hard-hitting beats and rhymes thicker than a cowboy's belt, others lack that strong chemistry or otherwise turn out formulaic. Chemistry is key when passing the baton off to another rapper; it may be why we don't have a ton of duos in Houston anymore, with all due respect to the likes of Dirty-N-Nasty, R.I.M., Rob Gullatte & Show, WhyJae & Nino Gotti, and others. Even those duos who aren't necessarily together, like Gullatte & Show, still hammer home the importance of ebbing off one another.

In lieu of one duo not coming together for a disc that no doubt would have whetted the appetites of Houston rap fans everywhere, it's time to reminisce on the greatest rap duos in the city's history. All apologies to the Geto Boys (a trio); Mike Jones & Magnificent (whose time together was brief, but yielded humorous results); and Big Pokey and Big Moe, obviously the largest tag team to be omitted from this list.

You can also apologize to Ro & Slim, since that combination is still in a fertile stage thanks to their four noted outings together, from "Gangsta" to now.

5. Slim Thug & ESG Around 2003, Slim Thug and E.S.G figured your everyday street gangsta and a Northside veteran should pair up. If you think about it, outside of probably Lil Keke, E.S.G. is one of Houston rap's glue guys, able to create with damn near anyone regardless of what side of 45 they lived on. Looking at them paired together makes a stark contrast. One has limbs that stretch like branches and a baritone that could lift a room. The other is short yet raps like he's ten feet tall with a piped-up voice that fills any arena you put it in.

Slim and ESG represent the first and second wave of Houston rap, typified by their 2002 collaboration album Boss Hogg Outlaws. "Getcha Hands Up" was their personal anthem, before they rounded out the album's 17 tracks with an all-star cast of characters from Bun B to Lil' O to Daz Dillinger.

Although their potential for future greatness was up there, Slim has been involved in crews from the beginning of his career but is a soloist at heart; same for ESG. At least we got a great album out of it, a colossal throwback jersey collage and even a second big single out of it, "This Is For My" with T-2.

4. Trae Tha Truth & Z-Ro Related or not, Trae Tha Truth and Z-Ro gave Southwest Houston an identity and then some with Guerrilla Maab. "Fondern & Main" still remains one of the greatest, yet still underrated, Houston rap songs in existence. Whether they were at each other's throats or indifferent to one another, the pair worked like Kobe and Shaq in the 2001 NBA playoffs.

Their crowning achievement as a duo will forever be their 2008 album It Is What It Is. If there was a Houston rap album equivalent of a 15-1 run to the title, this is it. Z-Ro and Trae knew one another's tendencies; namely how Z-Ro's drowsy take on isolation matched with Trae's knack to creep like a silent assassin in the background. It's a double-time rap album made between two men who have obviously been through hell and back in the years since.

The opening three tracks -- the guitar groans and threats of "Umm Hmm," the punched-up "Still Throwed" and "Who's The Man" -- are arguably the best three opening moments on a Houston rap album since UGK's greatest work, 1996's Ridin' Dirty. "Who's The Man" continued a time-honored Houston tradition of working a Lil Keke verse around a DIY mantra. "No Help" took Mary J. Blige's "Your Child," summed up everything you already knew about Ro and Trae, and then amplified it -- doing dirt all by their lonely, and feeling remorse for those they've lost along the way.

They're fourth all-time due to mostly what could have been. In the years following this 2008 masterpiece, Trae has become an ambassador for the city across the country and Ro has been transfixed by the idea being our version of The Wire's Omar Little. No more, no less.

3. Paul Wall & Chamillionaire Looking back now, Paul Wall and Chamillionaire were over-the-top goofballs on Swishahouse tapes, a can-you-top-this competitive streak that utilized the same flair Fat Pat and Lil Keke exhibited on their Screw tapes: Versace skeletons, buying fleets, outlandish balling on wax, which no doubt shaped the sort of goofy rhymes we get from RiFF RaFF on a daily basis.

Paul and Cham, along with Slim Thug, were the horses Swishahouse rode to national prominence. Whereas Screw tapes were released with a quickness and revolved around friends, Swishahouse tapes were halfway built on that No Limit cycle of album releases. Every major cultural event in the city needed a soundtrack, and Paul & Cham were the voices to some of those moments.

When the duo signed to Madd Hatta's Paid N Full, it was an early indie deal for two rappers who could have fought the world solo but sounded like Street Fighter's Ken and Ryu together. No one debut disc outfits itself quite like Get Ya Mind Correct, which even inspired arguably the greatest piece of Texans-related art in human history:

Yes, that.

Though it only yielded one real single, "N Luv With My Money," Mind Correct displayed everything you needed to know about these two cocky, confident and brash men. Paul could catch boppers in a cab if he wanted to, while Cham was parking a Bentley in the hottest part of your neighborhood. It sounded like a bombastic cartoon, all flash with little moral lessons here and there like "The Other Day."

Since then, there have been rumors of Cham writing for Paul, about their beef and that unauthorized Controversy Sells album -- "True," featuring Lil Flip, is the only memorable thing on it -- and more. Even after the split, neither one fell off to a point of obscurity. Instead, Cham became pissed off at the world and delivered a performance like Denzel in Man On Fire on Mike Jones' Mixtape Messiah and became a national name. Paul continued the hustle, stretched his persona even further for The People's Champ and hit No. 1.

Such a shame, considering "N Luv Wit My Money" is a charming piece of nostalgia now.

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