I need to create user profiles in the User Profile service, and I need to use the Client Side Object Model. The SP server is a on-Prem SharePoint 2013 server. How can this be implemented?
User Profiles cannot be created or Updated using CSOM as of now. You can update user profile properties using CSOM in SPO but not in On-Prem.
You can create user profile in SP 2013 server with Server Side Object Model.