Historicity of Other Religious Texts

there's been a lot of good info on here about the historic validity of the Jesus myth and other segments of the Christian bible - what about for other religions? A prime example is quite obviously Islam - how much of the Koran is based on historic events and/or 'real' people? What about for other religions, which unfortunately I'm not as well-versed on. Was the first Buddha a real person for example? Others?