Most Known Unknown is the eighth full-length studio album, as well as the second platinum album from Memphis rap group Three 6 Mafia. It was released on September 25, 2005, and is the follow-up to the 2003 album Da Unbreakables. This album is known for having some of Three 6 Mafia's biggest hits, including "Stay Fly" featuring Young Buck and 8Ball & MJG, "Poppin' My Collar" featuring Project Pat (though Pat's verse wasn't included in the first edition, but would later be included in the re-issue) and "Side 2 Side" featuring Bow Wow and Project Pat (with Bow Wow and Project Pat's verses, like the "Poppin' My Collar" remix, would not be used in the first edition, but would be released in the re-issue, along with another remix featuring Kanye West and a slightly different sounding melody). This album would prove to be their biggest success to date, topping the old success of the 2000 album When the Smoke Clears: Sixty 6, Sixty 1. The original version was released on a regular CD version as well as a DualDisc version. The re-release also had a bonus version, with two remixes of "Poppin' My Collar" and "Side 2 Side". A chopped and screwed version by Michael Watts was also released.
Most Known Unknown opened at number 3 on the Billboard 200 and number 1 on the R&B/Hip-hop charts with 125,000 copies sold. It was certified gold the week following its release on November 2, 2005, and reached platinum status by June 26, 2006.
Three 6 Mafia member Lord Infamous was notably missing from both the tracks and the album cover. Many rumors speculated that he either left the group or was kicked out; these rumors were put to rest when DJ Paul, Lord Infamous' half-brother, told sources that the reason for Infamous not being on the album was due to a stint in jail, leaving Crunchy Black, DJ Paul and Juicy J to be featured on the cover.