Who owns SPX index?

Could you please clarify who actually owns the SPX index? Is it a single entity, a consortium of companies, or does it belong to a broader financial organization? Furthermore, does ownership of the SPX index confer any special rights or privileges, or is it more of a collective benchmark that tracks the performance of a broad range of stocks? Understanding the ownership structure and implications of the SPX index would help us gain a deeper insight into its significance and influence in the financial markets.