Who started gangsta rap?

The first rap song to use the word 'Gangster' was probably 'Gangster Boogie' by Schooly D, released in 1984.

The first rap song to make reference to being in a gang was schooly D's 'P S K (What Does it Mean)' released in 1985.

'PSK' is cited by Ice-T as a major influence on his 1986 song '6 in the Mornin' which many consider the first 'Gangsta Rap' song.

Next would be Boogie Down Productions' album 'Criminal Minded' which contained the song '9mm Goes Bang' released in 1987.

Followed by Westcoast Rap Group N.W.A. (Eazy-E, Dr. Dre, Ice Cube, MC Ren, DJ Yella) with the album Straight Outta Compton with song such as: Straight outta Compton, Gangsta Gangtsa & F-ck tha Police in 1988.