Complex sentence: A student leader who went on to found the Black Consciousness Movement (BCM) which empowered and mobilized much of South Africa's urban black population, he has been called a martyr of the anti-apartheid movement.
Split into simpler sentences: A student leader who went on to found the Black Consciousness Movement (BCM), mobilizing much of South Africa's urban black population. Biko has been called a martyr of the anti-apartheid movement.