The Notorious B.I.G. and 2Pac
Cause: The so called "East Coast West Coast beef" is so sensationalized that the friendship between 2Pac and Biggie often gets overlooked. The two were quite friendly with each other, but the late-night shooting of 'Pac at New York's Quad studios changed everything. He soon accused Biggie and his entourage of having ties to the incident and the rest is, quite tragically, history.
What was once a friendship turned into a bitter rivalry played out on an international scale. Tensions escalated, diss songs were recorded, and the entire ordeal spiraled out of control. And in the end, we lost two of the greatest rappers ever.
Currently: Since Biggie's tragic death in 1997, neither case has been solved. The one positive that has come out of the situation is its status as a warning of what can happen if rap beef is taken too seriously.