It’s a toss-up between Verwoerd, who started the whole thing, and PW Botha, who could have ended it sooner but instead dug his heels in and made things so much worse. Also, he was in many ways responsible for: the homelands, Koevoet, the draft, the Border War, torture and murder…and then he went to his grave completely unrepentant for apartheid.
I think if there was no Verwoerd, some other white pol would have instituted it - Verwoerd was part of a whole movement, and he wasn’t the first PM under apartheid, Malan was.
Botha, on the other hand, took steps to actively consolidate all power in his own hands, and then acted as a stumbling block to any real change, preferring the tokens of homelands and the Tricameral Parliament system. If not for his stroke, who knows how many more years things would have dragged on.
Malan was, but Verwoerd was Malan’s Minister of Native Affairs, and bills like the Population Registration Act, the Bantu Education Act and the Group Areas Act came from his office, and he was the most hardline of Malan’s ministers on the apartheid question. That was the argument between he and Doenges, who wrote most of the Apartheid stuff.
Doenges said, “Look, the average Afrikaner is blue collar, unskilled, uneducated. If we don’t do something about the Black population, they’ll take all the jobs. So we have to set up Apartheid for a generation or two, to make sure that doesn’t happen, and then when the Afrikaner is on top, educated and rich, we can get rid of it, because the Blacks won’t be a threat anymore.”, but Verwoerd was a true believer, in the “Apartheid has to last forever because Blacks and Coloureds are naturally inferior to Whites, and it’s immoral not to have the laws reflect that.”
So I agree that apartheid would have happened regardless, but Verwoerd is responsible for making it harsher, more complete, and more repressive.
If you ever get the chance, you should read Herman Giliomee’s “The Last Afrikaner Leaders”, which is a look at the backgrounds and ideologies of Afrikaner leaders and how that influenced their decisions (he looks primarily at Verwoerd, Vorster, Botha, Van Slabbert, and De Klerk).
While Kruger was leader of the Transvaal, he was never ruler of South Africa. (He was also, not that it’s related, a flat earther, who got upset when he met the first person to sail alone around the world).