Who owns arbitrum?

Could you please elaborate on the ownership structure of Arbitrum? I'm particularly interested in understanding who exactly owns this cryptocurrency platform and what role they play in its operation. Is it a privately-held company, or does it have some form of decentralized governance? Additionally, could you also provide insights into the governance structure and how decisions are made within the organization? It would be great if you could provide a concise yet comprehensive overview of Arbitrum's ownership and governance setup.