Look at Mos Def and you see a poster child for the East Coast hip-hopper, Brooklyn division. But when he opens his mouth, whether plying his rhymes or just chatting, his eloquence shatters the preconceptions. What comes out is a surprising moral rectitude and religious focus.

"Black on Both Sides," his 1999 breakthrough album, has the same effect: witty title, and a look that's all about street cred. But the first words the listener hears are "Bismillah ar-Rahman ar-Raheem" ("In the name of God, the most gracious, the most merciful").

Islam has long played a prominent role in hip-hop. Among early rap groups like Afrika Bambata or mid-'80s groups like Poor Righteous Teachers and Big Daddy Kane, the Islamic inclinations were more implied than explicit. But by the '90s, Public Enemy was openly praising Nation of Islam leader Louis Farrakhan, and references to the 5 Percent Nation of Islam (a spin-off of the Nation of Islam) were popping up on albums by the Wu Tang Clan and Busta Rhymes. Especially when the topic is social justice, an Islamic understanding has been a hallmark of socially conscious hip-hop.

Mos Def, however, represents arguably the first time that an artist, solidly wedded to the orthodoxy of the religion, has stepped into mainstream popularity with a complete, well-articulated Islamic message as part and parcel of that popularity.

Born Dante Smith in 1974, the 27-year-old Brooklyn, N.Y., native first learned the importance of Islam from his father, who was a member of the Nation of Islam before becoming an active member in the community of Imam Warithdeen Muhammad (the son of Nation of Islam founder Elijah Muhammad who brought the Nation of Islam into orthodoxy in 1976).

Raised by his mother in Brooklyn, across the river from his father's home in New Jersey, Mos didn't receive a formal introduction to Islam until adolescence. "I got my first exposure to Islam when I was 13," says Mos. "My dad taught me how to make wudhu [the ritual ablution Muslims perform before prayer]."

It wasn't for another six years, when he was 19, that he took his shahada, the Muslim declaration of faith. He'd gotten there by reading and personal reflection and after getting to know other Muslim rappers, like Ali Shaheed Muhammad and Q-Tip of the group A Tribe Called Quest.

Since then, Islam has been the cornerstone of Mos' life and of his socially and spiritually themed music. "You're not gonna get through life without being worshipful or devoted to something," says Mos. "You're either devoted to your job, or to your desires. So the best way to spend your life is to try to be devoted to prayer, to Allah."

Tackling a broad swath of issues that include water rights, African American self-esteem, and the destiny of humankind, Mos enlightens the listener as well as entertains. Taking on such issues, he says, is an Islamic mandate. "If Islam's sole interest is the welfare of mankind, then Islam is the strongest advocate of human rights anywhere on Earth," says Mos.