Only one user can be the owner of an organization and it is usually the one that created the organization to begin with. If you are the owner of an organization, you are able to transfer your ownership to another user.
The owner has access to all the administration features, similar to a user with the 'admin' role. However, the owner also has access to billing, allowing them to view invoices, change billing information, and upgrade, downgrade, or cancel their D3M subscription.