He was not instrumental in the fall of apartheid. That was inevitable, utterly unsustainable, and collapsed of its own inertia, in much the same way communism in the USSR did.
The ANC and Mandela had nothing to do with that, but due to their position as the dominant political force - a dominance built on ciolence against their own people, with financial, political and ideological assistance from communist Russia, keen to exert influence in such a strategically located country - and too up the mantle by default, as 4 decades of violence from the ANC had effectively suppressed any other legitimate political rivalry.
So I ask you, when they weren't beating and killing blacks to get them to toe the line, exactly what did the ANC and Mandela do to bring about the fall of apartheid?