Imagine it's 1998. In the two years since the violent murders of iconic rappers 2Pac and The Notorious B.I.G., mainstream hip-hop has drifted away from the hard-edged style prevalent during the first half of the 1990s. Artists-cum-entrepreneurs like Sean "Puff Daddy" Combs and Master P now dominate the radio waves and MTV, polishing their gangsta roots with a commercial sheen. Having pulled their lyrical foci from America's ghettos-and placing them squarely in the realm of night clubs, Jacuzzis, Cristal and bling-hip-hop has become further removed from its old-school roots than ever before. It was two young rappers who, in the summer of that year, provided an intelligent alternative to the hip-hop status quo. Channeling old-school progenitors like Run-DMC and KRS-1 and the early-'90s jazz-rap collective Native Tongues, Mos Def and Talib Kweli released one of the greatest hip-hop albums of all time: Black Star. Just as Native Tongues' socially-conscious rhymes and jazz-inflected beats had brought a positivity to counterbalance gansta rap, Black Star's unique Afro-centrism and informed, philosophical style provided a foil to less substantive artists like Combs, catapulting the two rappers to the forefront of the hip-hop conscience and heavily influencing the mainstream and underground rap communities ever since.

That same iconoclasm will come to Waltham on April 7 when Mos Def-who in the seven years since the release of Black Star has crafted an acclaimed solo career and dabbled successfully in acting-brings his intricate, energetic flow to Gosman Gymnasium.

Born Dante Bez in Brooklyn in 1973, Mos Def reached maturity during the 1980s-the golden age of hip-hop. He was influenced not only by the vibrant music scene, but by the surrounding culture as well, developing a strong social conscience that would later influence his music. He began rapping at age nine and eventually formed the hip-hop ensemble Urban Thermo Dynamics in the early '90s, which released the single "My Kung Fu."

After that group dissolved, Mos Def was invited to join the Native Tongues crew and he appeared in songs by members De La Soul and Bush Babees. This provided the impetus for his rise in New York's underground hip-hop community and he soon became a regular performer at the famous Lyricist Lounge. He first collaborated with Talib Kweli in 1996 on the single "Fortified Live."

Mos Def and Talib Kweli were thrust into the national spotlight two years later with Black Star, named after black nationalist Marcus Garvey's Black Star shipping line. As its namesake suggests, the record sought to infuse the hip-hop community with a political conscience absent since the early days of Public Enemy, as well as to counteract the violence, negativity and even the pop sheen prevalent at the time.

One year later, Mos Def released his critically-acclaimed solo debut Black on Both Sides, which elaborated on Black Star's Afro-centric themes and jazz-rap beats by exploring genres like reggae, soul and hardcore punk.

Several cameos notwithstanding, Mos Def disappeared from music until last year, when he formed the all-black rock group Black Jack Johnson, which hoped to revive the legacy of '80s rockers Living Colour. Although they have not yet released a record, Black Jack Johnson appeared on several cuts of Mos Def's sophomore album, The New Danger, released last fall. While it received mostly lukewarm reviews, the album proved even more adventurous than Black on Both Sides.

Long before his rap career took off, however, Mos Def had built a solid rsum as an actor. After his graduation from high school in the late '80s, he landed a number of television roles-most notably on the short-lived The Cosby Mysteries. After the success of Black on Both Sides, he returned to acting, appearing on Broadway in the Pulitzer Prize-winning Topdog/Underdog, on television in MTV's Carmen: A Hip Hopera, and on the big screen in Monster's Ball, Bamboozled, The Italian Job and The Woodsman. He will star in an upcoming film adaptation of Douglas Adams' A Hitchhiker's Guide to the Galaxy.