There's a new version of the Owners API. We've redesigned our contacts API and it is out now in developer preview. Check out the new API
HubSpot uses owners to assign CRM object records (contacts, companies, deals, tickets, and engagements) to specific people in your organization.
Use case for this API: The Owners API can be used to get the IDs of the owners you have in HubSpot, allowing an integration to assign records.