Who were Andrew Carnegie's mentors?

Likely any of the philosophers Baruch Spinoza (1632-1677), John Locke (1632-1704), and Pierre Bayle (1647-1706) and mathematician Isaac newton

It depends on your meaning of "mentor"

Andrew Carnegie enjoyed reading from a young age and secured himself access to books (not everyone had access)

I live a few doors up from his birthplace in his beloved hometown. Remarkable man.