Sponsor, PM, team, stakeholders

The sponsor is the senior person who champions the project, provides funding, owns the business case, and clears organisational obstacles. The sponsor authorises the project (typically by signing the project charter) and accepts the final benefits. The sponsor does not run the project day-to-day — that's the PM.

The project manager is the person assigned by the performing organisation to lead the team that is responsible for achieving the project objectives. PMBOK 8e calls out a broader 'project management team' — the PM plus any people who help with management activities (planning, controlling, reporting). The PM is accountable for the outcome; the team is responsible for the work.

Stakeholders are anyone who can affect, be affected by, or perceive themselves to be affected by the project. That includes the customer, end users, the sponsor, regulators, suppliers, the PM's own functional manager, and even people who think the project will harm them. PMBOK is generous with the definition: if they think they're a stakeholder, they probably are.