Mathenge was educated at Strathmore School, He rose to fame in 1999 through a star-search contest on Kenya's urban music station 98.4 Capital FM, which he won with his original song "Megarider." The song was about a penniless young man who is trying to seduce a woman but only has enough money for Kenya Bus tickets, and not the rich lifestyle she desires. He later recorded the track with producer Tedd Josiah and it went on to be hot on the charts for weeks. This was the turning point in his musical career. He went on to sign with the Ogopa Deejays label in 2001 and collaborated with artists such as the late E-Sir on "Boomba Train," and Amani on the regional hit "Ninanoki" in 2002 which broke Kenyan chart records by remaining nearly four months at number one. He has gone on to tour across the East African region and in the U.S.A and U.K. In 2004, he released his debut album On Fire. In 2004, Mathenge married Ogopa Deejays label mate Wahu Kagwi. They have two daughters, Tumiso who was born in 2006, and Nyakio born in 2013. He is also an architect and graduated from the University of Nairobi. South African pop group Jamali's wildly popular song "Maisha" was the subject so much controversy with allegations that Jamali had stolen the song from Nameless. The dispute was settled when Jamali released their CD/DVD of Yours Fatally and credited Nameless as one of the writers of "Maisha". In August 2007, he appeared on the list of 100 most influential Kenyans as selected by The Standard newspaper.