Well, he crushed competition and ruined men's lives who would not join him, and heralded the way for monopolization and a corporatism which bought off government and destroyed free enterprise for those who were not the mega-corporations, not to mention practices which were none too generous to workers. Was he alone, no. Was he the first, no, as you have the barons of the railroad and mining giants and so forth. But he was one of the Big Boys come the end of the 19th century and beginning of the 20th century.
I don't think he's the most hated man in America now, and he did manage to reform him image in I believe the 1920's (basically in a series of filmed photo-ops which were highly fake, but that was not known to the public, and after which he'd hand out a "Rockefeller Dime". He also handed out those dimes at public appearances not filmed. I recall one film which purported to show his first plane ride and Rockefeller was never actually in the plane; they just filmed it taking off.)