Who started the Roman Catholic Church? It's a fallacious question & reveals a gross ignorance of church history. Never at any point was Rome & its magisteriam "the church." It's was once in the church, or part of the church, but was never "the church."
The real question is who led Rome & its followers into the way of destruction & apostasy? The answer is simple. It was a succession of reprobate power hungry Bishops in Rome who gradually over time increased their own power by lies, deceit, murder, & forgeries, & the introduction of false teachings & growing superstitions. It wasn't one single bishop, but many of them who over time led Rome into apostasy & the sniffing out of its candlestick.