Regardless, as Mikey said, before he invaded the Sacred Realm he was trying to make an alliance with the King of Hyrule, meanwhile terrorizing the guardians of the spiritual stones to pressure them into giving them to him, and plotting to kill the King anyway.
That's what made me feel as if his TWW sob story had nothing to do with his original plans, and that he was just giving that speech to make Link lower his guard(which worked). He was plotting to do evil s**t since the beginning, such as killing the king. He even tells Link before getting the ToP that he plans to rule the world.
So, was it the ToP that corrupted him? No, it just gave him the means to accomplish his goal, which is and probably always has been, to rule the world.
Did some demon named Ganon corrupt him? No, because Ganondorf and Ganon are one in the same person, with Ganon merely being a nickname for Ganondorf in universe as mentioned in ALttP and HH among other sources, with his pig demon form being to Vaati's Wind Demon form what his human Gerudo form is to Vaati's human Minish form.
It was him. HIS desires. HIS plans.
Just like in real life, some people are born monsters. To say that Ganondorf was some nice guy that got corrupted is not only nonsensical with what we know about the games and lore, but makes his presence in games like OoT pointless if he's somesort of pawn, not to mention that there is no evidence of such a thing.