Who is the greatest rapper of all time? What does that title mean? Times change. Skills fade. New greats emerge. Old ones decline. How can anyone crown the best emcee when so many great ones are still working? To be as fair and thorough as possible, here are some ground rules. Eligible artists must have been active for at least 10 years and have released at least two albums. They were evaluated for originality, longevity, lyrics, cultural impact, flavor, battle skills, body of work, poetic value, substance, versatility, vocal presence, live performance, flow, delivery, and influence. These 50 emcees have done everything it takes to make a play for the throne:

50 of 50 Gift of Gab WireImage / Getty Images Gift of Gab's flow is smooth as ice. His poetics are audio tattoos. Though Gift and Blackalicious comrade Chief Xcel never strayed far enough from their recipe to line their walls with plaques, their body of work won the hearts of fans and critics from coast to coast.​ Essential: "Nia"

49 of 50 Guru WireImage / Getty Images It's mostly the voice. It was unmistakable. As the voice of Gang Starr (DJ Premier helmed the duo's production department), Guru was instrumental in creating one of the greatest hip-hop duos of all time. Extra credit goes to Baldhead Slick for being one of the premier jazz rappers. Who could forget that velvet voice? Essential: "Daily Operation"

48 of 50 Prodigy WireImage / Getty Images Before the G-Unit tattoos, before the Jay-Z battle, before the Havoc feud, Prodigy was a pivotal player in East Coast rap. P and his partner in rhyme Hav brought dun talk to the Queensbridge projects. Outside The Mobb, Prodigy went on to become a solo force. He teamed up with producer Alchemist on 2007's "Return of the Mac" and 2013's "Albert Einstein." Essential: "The Infamous (with Mobb Deep)"

47 of 50 Posdnuos WireImage / Getty Images At a time when gangsta rap was the order of the day, Posdnuos and his De La Soul cohorts crashed the party with a smile and some daisies. Essential: "Is Dead"

46 of 50 Jadakiss WireImage / Getty Images A street-wise lyricist, Jadakiss has maintained a startling level of consistency since the days of L-O-X. Aside from his raspy flow and his ability to dismantle anyone on a track, Jada is famous for threatening to throw a refrigerator at Diddy over a publishing dispute. Essential: "Kiss of Death"

45 of 50 Bun B Getty Images for The Recording A / Getty Images Bun B emits charm and charisma on wax and in person. Bun's technique, leadership, and cultural impact earned him the respect of peers and fans. The 5 mic winning showed he can still hang with the best of 'em. Essential: "Ridin' Dirty (with UGK)"

44 of 50 T.I. WireImage / Getty Images Rappers are obsessed with royalty, many declaring themselves king at some point in their career, but few have taken the proclamation as seriously as T.I. The Kang gained credibility via the cosign of fellow kings such as Scarface and Bun B, but he still had to make good on the title. So he did, dropping hit after hit, juking past rivals, and keeping the street happy simultaneously. T.I.'s best songs are often the ones where the trap meets the charts. Thanks to this foolproof recipe, T.I. has enjoyed multiple platinum successes, including the million-selling "King" and double platinum "Paper Trail." ​ Essential: "Trap Muzik"

43 of 50 Beanie Sigel WireImage / Getty Images With a distinctive delivery and a tested battle pedigree, Beans followed in the long line of Philly-bred greats. He was one of Roc-a-Fella's brightest alongside Jay-Z and Kanye West. There must be a special formula in the waters of Philadelphia. Essential: "The Truth"

42 of 50 DMX WireImage / Getty Images

DMX made a name for himself with the ever-peculiar mix of spirituality and passion. 1998 was a highlight in his career, as the Yonkers emcee released two albums in one year. Both flew straight to numero uno. Essential: "It's Dark and Hell Is Hot"

41 of 50 Snoop Dogg Andrew Chin / Getty Images Not too many rappers have been able to create mainstream hits while still keeping it "G." Apart from wielding the slickest of slick flows, Snoop has supplied some of the most captivating hooks hip-hop has ever witnessed. Essential: "Doggystyle"

40 of 50 Queen Latifah Tim Mosenfelder / Getty Images Queen Latifah wasn't the first female rapper, but she was definitely the first to become a star. Her third album, "Black Reign," became the first by a female emcee to be certified gold. Latifah's commercial success kicked down doors for future stars such as Da Brat, Lauryn Hill, and Nicki Minaj. Essential: "All Hail the Queen"

39 of 50 Kendrick Lamar Getty Images for Clara Lionel Fo / Getty Images Kendrick Lamar emerged as arguably the best rapper of the 2010s, following the release of two critically acclaimed albums, "good kid, m.A.A.d city" and "To Pimp a Butterfly." His pre-Aftermath/Interscope project, "Section.80," wasn't too shabby, either. Lamar brought a refreshing sense of leadership and innovation to the game, challenging his peers, highlighting societal ills, and, ultimately, pining for a hopeful resolve.

38 of 50 Q-Tip Getty Images for The Meadows Music & Arts Festival / Getty Images As Tribe's lead emcee, Q-Tip helped pioneer jazz rap. Tip promoted Afrocentric ideals and social discourse without ever raising his voice. Essential: "Midnight Marauders"

37 of 50 Kanye West Getty Images for The Meadows / Getty Images Kanye West walks around with a Texas-size boulder on his shoulder, but he has the skills to back up the drama. West is arguably the best producer on the mic. His technique has evolved over the years, and his albums are topically diverse. His influence is ubiquitous. Essential: "Late Registration"

36 of 50 Busta Rhymes FilmMagic / Getty Images One of the founding principles of emceeing is the ability to move the crowd. Who can say they've never been compelled to move to the beat by Busta's favorite grunt: "Whoo-HA!" Extra points for being the most energetic live performer in hip-hop history. Essential: "Extinction Level Event: Final World Front"

35 of 50 Lupe Fiasco Scott Legato / Getty Images When your first hit is about skateboarding and you ka kun ka kun your way to the top of the game while eating Kanye West on his own track, your future certainly looks bright as all seven skies. Emperor Lu has toyed with career suicide, but he still lives to influence a generation of lyricists such as J. Cole and Kendrick Lamar. Essential: "Food & Liquor"

34 of 50 Raekwon WireImage / Getty Images Although the "chef" in Raekwon the Chef has more to do with white meat than soul food, Rae helped create the recipe for mafioso rap in the '90s. Apart from his obvious influence on many of today's emcees, he is also the author of one of the best hip-hop albums of all time, "Only Built 4 Cuban Linx." Essential: "Only Built 4 Cuban Linx"

33 of 50 Kool Moe Dee Paras Griffin / Getty Images With his deadly combination of wit and grit, Kool Moe Dee helped write the blueprint for what would eventually become known as battle rap. Essential: "How Ya Like Me Now"

32 of 50 Canibus WireImage / Getty Images Military vet Canibus is known for his esoteric psych-rap transcendence. When he's not battling an unidentified foe, he's pondering UFO conspiracy theories and the nature of chicken parmesan. Anyone who can battle LL Cool J and Eminem in the same lifetime and still stand is a man of valor. Essential: "Mic Club: The Curriculum"

31 of 50 Royce da 5' 9" WireImage / Getty Images Anyone who's ever driven a standard one-gear car understands the mind of Royce da 5' 9". Nickel Nine knows only one way to steer the mic, and that's to subdue every beat he comes in contact with. A battle vet, Royce thrives on competition. He's teamed up with Eminem as Bad Meets Evil and plies his trade as one-fourth of the supergroup Slaughterhouse, alongside Joe Budden, Crooked I, and Joell Ortiz. Essential: "Death Is Certain"

30 of 50 Killer Mike WireImage / Getty Images Killer Mike is the new school Ice Cube: the voice of a minister, the attitude of a Panther, and the delivery of a cannonball. Mike's versatility is one of his best weapons. He rocks party jams and militant anthems with the same gusto.

29 of 50 Talib Kweli Getty Images for Ozy Fusion Fest 2017 / Getty Images Talib Kweli was drawn to writing at an early age, having grown up with college professors as parents. Kweli extends those early lessons to his art, using hip-hop as a platform to enlighten and empower his community.​ Essential: "Quality"

28 of 50 Ghostface Killah Getty Images for The Meadows Music & Arts Festival / Getty Images Ghostface is one of the most imaginative storytellers of our time. He's also the most consistent album maker in hip-hop, with a deep, rich catalog of great albums. Essential: "Supreme Clientele"

27 of 50 AZ Mika-photography/Wikimedia Commons/CC SA BY 3.0 AZ, who debuted on Nas' 1994 hit song "Life's a B***h," is arguably the most underrated rapper ever. Too tough to sell out, his "intelligent thug" persona sets him aside from his peers. Essential: "Doe or Die"

26 of 50 MC Lyte Brad Barket / Getty Images Brooklyn's own MC Lyte is the complete package. She made her entrance by helping Sinead O'Connor to a dance hit, throwing flames at a cheating boyfriend, and railing against copycat rappers, all at the same time. Essential: "Lyte as a Rock"

25 of 50 Big Pun Hiroyuki Ito / Getty Images Despite his large frame, Big Pun's fun, fast, and feisty rhymes kept him light years ahead of his peers. He was also the first solo Latino rapper to go platinum. Essential: "Capital Punishment"

24 of 50 LL Cool J Getty Images for The Meadows Music & Arts Festival / Getty Images LL's longevity has never been disputed—he hasn't been able to "Live Without His Radio" since 1985—and, unlike other '80s icons, Cool J has managed to reinvent his style over the years to reflect the current hip-hop landscape. Essential: "Mama Said Knock You Out"

23 of 50 Big L Gunned down in his prime at 24 on Feb. 15, 1999, the rest of Big L's talent followed him to the grave. But he left behind enough material to make a case as one of the most talented poets in hip-hop history. Essential: "The Big Picture"

22 of 50 Masta Ace WireImage / Getty Images Surrounded by Juice Crew vets Marley Marl, MC Shan, Big Daddy Kane, Biz Markie, Roxanne Shante, and Craig G, Masta Ace was an early unsung talent. His wit, wordplay, and consistency eventually earned him a spot among the greats. Essential: "Disposable Arts"

21 of 50 Pharoahe Monch WireImage / Getty Images Through his panoramic vision and hyper-realistic narratives, Pharoahe Monch solidified a reputation as one of hip-hop's prominent lyricists. Essential: "Internal Affairs"

20 of 50 Redman Getty Images for SXSW / Getty Images Redman doesn't get the credit he deserves, but he's inspired a handful of other greats on this list, including Eminem. Sometimes satirical, sometimes silly, Redman is one of the liveliest storytellers of his era.

Essential: "Muddy Waters"

19 of 50 Common J. Countess / Getty Images An ingenuous street poet, master storyteller, and battle-worn warrior, Common has kept Chi-town hip-hop's flag flying high for two decades. Essential: "Resurrection"

18 of 50 Lauryn Hill Scott Legato / Getty Images After years as a member of the Fugees, Lauryn Hill finally broke out as a solo star with 1998’s "The Miseducation of Lauryn Hill." Some of the album’s most unforgettable tunes are poignant tributes to motherhood, relationships, and culture. Lauryn is one of the greatest emcees of all time, male or female. Essential: "The Miseducation of Lauryn Hill"

17 of 50 GZA / Genius Scott Dudelson / Getty Images Armed with sharp metaphors and a smooth flow, Shaolin swordsman GZA is one of the most cerebral emcees in the Wu family.

Essential: "Liquid Swords"

16 of 50 Black Thought Redferns / Getty Images Black Thought is a surgeon of emceeing, reaching only for the most incisive effect that each line and verse, each metaphor and punchline, can convey, and applying his skill accordingly. If you listen closely you might hear him feeling around his tool box for just the right flow, the right vocal inflection, the right rhyme sequence. He always seems to find it. Essential: "Illadelph Halflife"

15 of 50 Chuck D Getty Images for Rush Philanthropic Arts Foundation / Getty Images Lyrical with a militant message and a take-no-prisoners persona, Chuck D remains a hugely influential figure in the game. Essential: "It Takes a Nation of Millions to Hold Us Back"

14 of 50 Mos Def Nicholas Hunt / Getty Images Before he caught the acting bug, Mos Def made an indelible impression on hip-hop with lyrics so clean they made your parents boogie. Essential: "Black on Both Sides"

13 of 50 Andre 3000 FilmMagic / Getty Images He raps, sings, acts, and even dabbles in guitar. Andre 3000 is hip-hop's renaissance man. Although he's released no solo albums, Dre has developed a reputation for stealing the show with nearly every guest appearance. Essential: "Aquemini"

12 of 50 KRS-One Scott Dudelson / Getty Images The Teacha transformed the brusque violence of street life into a story of uplift and self-awareness, starting with BDP's incendiary debut, "Criminal Minded."

Essential: "By All Means Necessary (with Boogie Down Productions)"

11 of 50 Slick Rick Scott Dudelson / Getty Images Despite myriad run-ins with the INS and jail stints, Ricky Walters managed to hold down the storytelling department like no other. Essential: "The Great Adventures of Slick Rick"

10 of 50 Ice Cube FilmMagic / Getty Images Politically salient with an in-your-face voice, Ice Cube developed a cult-like following by favoring substance over style. He's also the only man who went to war with NWA and came out on top.​

Essential: "Death Certificate"

09 of 50 Big Daddy Kane Paras Griffin / Getty Images Big Daddy Kane is the original king of swagger. Charismatic and confident on the mic, Kane entertained the world with his peculiar flair and stylish wardrobe. Rappers such as Jay-Z, Biggie, and Snoop later adopted his player persona. Essential: "Long Live the Kane"

08 of 50 Kool G Rap WireImage / Getty Images The next time your favorite emcee commits a double-homicide on wax, blame it on Kool G Rap. Why? He's the grandfather of hardcore hip-hop. Some of the grittiest street tales in rap grew out of G Rap's rhyme book. Essential: "Wanted: Dead or Alive (with DJ Polo)"

07 of 50 Eminem Scott Legato / Getty Images Eminem is a once-in-a-generation talent. His dystopian rhymes, complex flow, experimental wordplay, and meticulous phrasing make him one of the best emcees of all time. Essential: "The Marshall Mathers LP"

06 of 50 Scarface Tibrina Hobson / Getty Images Only a handful of emcees have managed to sustain their alignment with the streets regardless of mainstream plaudits. Scarface is at the top of that list. His street tales and poetic raps are constant reminders that Brad Jordan is the voice of the hood.

Essential: "The Diary"

05 of 50 2Pac Raymond Boyd/Michael Ochs Archives/Getty Tupac Shakur is the most influential hip-hop artist of all time. Even in death, 2Pac remains a transcendental rap figure. Afeni's baby is often imitated but never duplicated. Essential: "Me Against the World"

04 of 50 Jay-Z Tim Mosenfelder / Getty Images Jay-Z changed the game on and off wax. Musically, he inspired a host of young emcees eager to learn how to hustle their flow. Business-wise, he inspired a group of hustlers-turned-trappers. Peep his flawless flow and double-entendres. That marketing plan was him. Essential: "Reasonable Doubt"

03 of 50 The Notorious B.I.G. Adger Cowans/Getty Images The Notorious B.I.G. was the complete emcee. He had the stories, the hits, the unforgettable guest rhymes, the lyrics, and a great body of work to leave a lasting mark. Biggie had enough pizzazz to sway audiences young and old. His effortless wit and unparalleled flow made him one of the greatest rappers of our time. Essential: "Ready to Die"

02 of 50 Rakim Scott Dudelson / Getty Images While others bragged about their guns, Rakim celebrated his skills. Before Rakim, hip-hop was all about nursery rhymes. He changed the game by introducing multisyllabic rhymes and a slew of new slangs. A smooth, laid-back flow and positive messages are the hallmarks that make Rakim half of one of rap's greatest duos and a contender for the ultimate crown in hip-hop. Essential: "Paid in Full (Eric B. & Rakim)"