Where you have those 1000 user record details in csv or from any legacy system you want to create? Keep those 1000 users in a csv file, with all mandatory fields in the csv fiel, then use Apex Dataloader/Workbench or any other data import tool to import users in to the system.
Keep those 1000 users in a csv file, with all mandatory fields in the csv fiel, then use Apex Dataloader/Workbench or any other data import tool to import users in to the system.
Check this link for details about Data management in salesforce - https://help.salesforce.com/HTViewQuickStarts?id=000113376